При нажатии кнопка не работает

1. НИКОГДА НЕ ИЗМЕНЯЙТЕ код, сгенерированный Qt Designer, НИКОГДА.
   Создайте другой класс, который наследуется от соответствующего виджета, и используйте созданный класс для его заполнения.

2. У вас проблемы с абсолютным позиционированием виджетов. Вы виджетами, которые унаследованы от QGroupBox, накрываете все другие виджеты.

3. Научитесь использовать менеджеры компоновки:
   Управление макетом / Layout Management

import sys
from PyQt5 import QtCore, QtGui, QtWidgets


class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(811, 480)
        self.centralwidget = QtWidgets.QWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")
        
        self.horizontalSlider = QtWidgets.QSlider(self.centralwidget)

        self.horizontalSlider.setGeometry(QtCore.QRect(20, 40, 121, 31))
        self.horizontalSlider.setOrientation(QtCore.Qt.Horizontal)
        self.horizontalSlider.setObjectName("horizontalSlider")
        
        self.groupBox = QtWidgets.QGroupBox(self.centralwidget)
        self.groupBox.setGeometry(QtCore.QRect(10, 10, 141, 131))
        self.groupBox.setObjectName("groupBox")
        self.label = QtWidgets.QLabel(self.groupBox)
        self.label.setGeometry(QtCore.QRect(40, 70, 47, 13))
        self.label.setObjectName("label")
        
        self.radioButton = QtWidgets.QRadioButton(self.centralwidget)
        self.radioButton.setGeometry(QtCore.QRect(20, 150, 141, 91))
        self.radioButton.setObjectName("radioButton")
        self.radioButton_2 = QtWidgets.QRadioButton(self.centralwidget)
        self.radioButton_2.setGeometry(QtCore.QRect(20, 200, 141, 91))
        self.radioButton_2.setObjectName("radioButton_2")
        self.radioButton_3 = QtWidgets.QRadioButton(self.centralwidget)
        self.radioButton_3.setGeometry(QtCore.QRect(20, 250, 141, 91))
        self.radioButton_3.setObjectName("radioButton_3")
        
        self.groupBox_2 = QtWidgets.QGroupBox(self.centralwidget)
        self.groupBox_2.setGeometry(QtCore.QRect(10, 150, 141, 181))
        self.groupBox_2.setObjectName("groupBox_2")
        self.lineEdit = QtWidgets.QLineEdit(self.centralwidget)
        self.lineEdit.setGeometry(QtCore.QRect(20, 350, 111, 21))
        self.lineEdit.setObjectName("lineEdit")
        self.pushButton = QtWidgets.QPushButton(self.centralwidget)
        self.pushButton.setGeometry(QtCore.QRect(40, 390, 75, 23))
        self.pushButton.setObjectName("pushButton")
        
        self.groupBox_3 = QtWidgets.QGroupBox(self.centralwidget)
        self.groupBox_3.setGeometry(QtCore.QRect(10, 330, 141, 91))
        self.groupBox_3.setObjectName("groupBox_3")
        
        MainWindow.setCentralWidget(self.centralwidget)
        
        self.menubar = QtWidgets.QMenuBar(MainWindow)
        self.menubar.setGeometry(QtCore.QRect(0, 0, 811, 21))
        self.menubar.setObjectName("menubar")
        self.menuFile = QtWidgets.QMenu(self.menubar)
        self.menuFile.setObjectName("menuFile")
        MainWindow.setMenuBar(self.menubar)
        
        self.statusbar = QtWidgets.QStatusBar(MainWindow)
        self.statusbar.setObjectName("statusbar")
        MainWindow.setStatusBar(self.statusbar)
        
        self.action = QtWidgets.QAction(MainWindow)
        self.action.setObjectName("action")
        self.action_2 = QtWidgets.QAction(MainWindow)
        self.action_2.setObjectName("action_2")
        self.actionExit = QtWidgets.QAction(MainWindow)
        self.actionExit.setObjectName("actionExit")
        
        self.menuFile.addAction(self.action)
        self.menuFile.addAction(self.action_2)
        self.menuFile.addAction(self.actionExit)
        self.menubar.addAction(self.menuFile.menuAction())

        self.retranslateUi(MainWindow)
        QtCore.QMetaObject.connectSlotsByName(MainWindow)

    def retranslateUi(self, MainWindow):
        _translate = QtCore.QCoreApplication.translate
        MainWindow.setWindowTitle(_translate("MainWindow", "MainWindow"))
        self.groupBox.setTitle(_translate("MainWindow", "Size brush"))
        self.label.setText(_translate("MainWindow", "TextLabel"))
        self.radioButton.setText(_translate("MainWindow", "Square"))
        self.radioButton_2.setText(_translate("MainWindow", "Triangle"))
        self.radioButton_3.setText(_translate("MainWindow", "Circle"))
        self.groupBox_2.setTitle(_translate("MainWindow", "Style brush"))
        self.pushButton.setText(_translate("MainWindow", "OK"))
        self.groupBox_3.setTitle(_translate("MainWindow", "Colors"))
        self.menuFile.setTitle(_translate("MainWindow", "File"))
        self.action.setText(_translate("MainWindow", "Add file"))
        self.action_2.setText(_translate("MainWindow", "Save file"))
        self.actionExit.setText(_translate("MainWindow", "Exit"))

#        self.pushButton.clicked.connect(self.test)
#               
#    def test(self):
#        print("hello")

# ??? Form, Window = uic.loadUiType("interface.ui")                   # ???

class MainWindow(QtWidgets.QMainWindow, Ui_MainWindow):
    def __init__(self):
        super().__init__()
        self.setupUi(self)
        
        layout_grb_1   = QtWidgets.QVBoxLayout(self.groupBox)
        layout_grb_1.addWidget(self.horizontalSlider, alignment=QtCore.Qt.AlignCenter)
        layout_grb_1.addWidget(self.label, alignment=QtCore.Qt.AlignCenter)
        
        layout_grb_2   = QtWidgets.QVBoxLayout(self.groupBox_2)
        layout_grb_2.addWidget(self.radioButton)
        layout_grb_2.addWidget(self.radioButton_2)        
        layout_grb_2.addWidget(self.radioButton_3)        

        layout_grb_3   = QtWidgets.QVBoxLayout(self.groupBox_3)
        layout_grb_3.addWidget(self.lineEdit, alignment=QtCore.Qt.AlignCenter)
        layout_grb_3.addWidget(self.pushButton, alignment=QtCore.Qt.AlignCenter)        
        
        self.pushButton.clicked.connect(self.test)

        self.lineEdit.setText("Hello Mihusa")
               
    def test(self):
        print(f"hello: {self.lineEdit.text()}")
        

if __name__ == "__main__":
    import sys
    app = QtWidgets.QApplication(sys.argv)
    window = MainWindow()
    window.show()
    sys.exit(app.exec())