Improve compatibility with unofficial releases before Cura 5.0

Some versions of Cura tried to use the system-installed PyQt6 when they should still be using PyQt5 (which can be installed in parallel)

Author: fieldOfView

SidebarGUIPlugin.py

@@ -8,9 +8,13 @@
 from UM.Logger import Logger
 
 try:
+    from cura.ApplicationMetadata import CuraSDKVersion
+except ImportError: # Cura <= 3.6
+    CuraSDKVersion = "6.0.0"
+if CuraSDKVersion >= "8.0.0":
     from PyQt6.QtCore import QUrl
     from PyQt6.QtQml import qmlRegisterSingletonType
-except ImportError:
+else:
     from PyQt5.QtCore import QUrl
     from PyQt5.QtQml import qmlRegisterSingletonType
 

SidebarGUIProxy.py

@@ -6,8 +6,12 @@
 from UM.FlameProfiler import pyqtSlot
 
 try:
+    from cura.ApplicationMetadata import CuraSDKVersion
+except ImportError: # Cura <= 3.6
+    CuraSDKVersion = "6.0.0"
+if CuraSDKVersion >= "8.0.0":
     from PyQt6.QtCore import QObject, QRectF
-except ImportError:
+else:
     from PyQt5.QtCore import QObject, QRectF
 
 try: