Qt5->Qt6: Fix cause of stack-overflow errors for newer Python/Qt.

part of CURA-8591

cura/Settings/ContainerManager.py

@@ -47,11 +47,11 @@ class ContainerManager(QObject):
     def __init__(self, application: "CuraApplication") -> None:
         if ContainerManager.__instance is not None:
             raise RuntimeError("Try to create singleton '%s' more than once" % self.__class__.__name__)
-        ContainerManager.__instance = self
         try:
             super().__init__(parent = application)
         except TypeError:
             super().__init__()
+        ContainerManager.__instance = self
 
         self._container_name_filters = {}  # type: Dict[str, Dict[str, Any]]
 

cura/Settings/ExtruderManager.py

@@ -31,9 +31,9 @@ class ExtruderManager(QObject):
 
         if ExtruderManager.__instance is not None:
             raise RuntimeError("Try to create singleton '%s' more than once" % self.__class__.__name__)
-        ExtruderManager.__instance = self
 
         super().__init__(parent)
+        ExtruderManager.__instance = self
 
         self._application = cura.CuraApplication.CuraApplication.getInstance()
 

plugins/USBPrinting/USBPrinterOutputDeviceManager.py

@@ -30,9 +30,10 @@ class USBPrinterOutputDeviceManager(QObject, OutputDevicePlugin):
     def __init__(self, application, parent = None):
         if USBPrinterOutputDeviceManager.__instance is not None:
             raise RuntimeError("Try to create singleton '%s' more than once" % self.__class__.__name__)
-        USBPrinterOutputDeviceManager.__instance = self
 
         super().__init__(parent = parent)
+        USBPrinterOutputDeviceManager.__instance = self
+
         self._application = application
 
         self._serial_port_list = []

plugins/XmlMaterialProfile/PluginInfo.py

@@ -5,9 +5,9 @@ class PluginInfo(PluginObject):
     __instance = None # type: PluginInfo
 
     def __init__(self, *args, **kwags):
-        super().__init__(*args, **kwags)
         if PluginInfo.__instance is not None:
             raise RuntimeError("Try to create singleton '%s' more than once" % self.__class__.__name__)
+        super().__init__(*args, **kwags)
         PluginInfo.__instance = self
 
     @classmethod