title: QSizePolicy issue in PySide6
body: <p>I'm trying to centre the buttons in a QToolBar using two dummy spacer widgets, but I'm not able to set the size policy for some reason. Not sure what I'm doing wrong as the error says I'm passing a tuple, which should be accepted (last line from output), but apparently is not. Works ok without the size policy lines, but obviously I don't get the desired outcome.</p>
  <p>Example:</p>
  <pre><code>import sys
  from PySide6.QtWidgets import *
  from PySide6.QtGui import *
  from PySide6.QtCore import *
  from __feature__ import snake_case, true_property
  
  
  class MainWindow(QMainWindow):
      def __init__(self):
          super().__init__()
          self.set_ui()
  
      def set_ui(self):
          self.resize(640, 480)
          self.window_title = &quot;Main Window&quot;
          central = QWidget()
          layout = QHBoxLayout(central)
          tool_bar = MainToolBar()
          self.add_tool_bar(Qt.ToolBarArea.TopToolBarArea, tool_bar)
          self.central_widget = central
  
  
  class MainToolBar(QToolBar):
      def __init__(self):
          super().__init__()
  
          group = QActionGroup(self)
          
          home = QAction(&quot;Home&quot;, group)
          page2 = QAction(&quot;Page 2&quot;, group)
          page3 = QAction(&quot;Page 3&quot;, group)
  
          left_spacer = QWidget()
          left_spacer.size_policy = (QSizePolicy.Expanding, QSizePolicy.Expanding)
          right_spacer = QWidget()
          right_spacer.size_policy = (QSizePolicy.Expanding, QSizePolicy.Expanding)
  
          self.add_widget(left_spacer)
          for action in group.actions():
              action.checkable = True
              self.add_action(action)
          self.add_widget(right_spacer)
  
  if __name__ == &quot;__main__&quot;:
      app = QApplication([])
      window = MainWindow()
      window.show()
      sys.exit(app.exec())
  </code></pre>
  <p>Output:</p>
  <pre><code>Traceback (most recent call last):
    File &quot;/Users/Vlad/Documents/test.py&quot;, line 46, in &lt;module&gt;
      window = MainWindow()
    File &quot;/Users/Vlad/Documents/test.py&quot;, line 11, in __init__
      self.set_ui()
    File &quot;/Users/Vlad/Documents/test.py&quot;, line 18, in set_ui
      tool_bar = MainToolBar()
    File &quot;/Users/Vlad/Documents/test.py&quot;, line 34, in __init__
      left_spacer.size_policy = (QSizePolicy.Expanding, QSizePolicy.Expanding)
  TypeError: 'PySide6.QtWidgets.QWidget.size_policy.fset' called with wrong argument types:
    PySide6.QtWidgets.QWidget.size_policy.fset(tuple)
  Supported signatures:
    PySide6.QtWidgets.QWidget.size_policy.fset(PySide6.QtWidgets.QSizePolicy)
    PySide6.QtWidgets.QWidget.size_policy.fset(PySide6.QtWidgets.QSizePolicy.Policy, PySide6.QtWidgets.QSizePolicy.Policy)
  </code></pre>