Addon Manager: Qt6 migration part 1, use PySide

Migrate all uses of "import PySide 2" to use "import PySide" so that the
FreeCAD-provided wrappers can switch between Qt versions.

src/Mod/AddonManager/addonmanager_utilities.py

@@ -32,7 +32,7 @@ from typing import Optional, Any
 
 from urllib.parse import urlparse
 
-from PySide2 import QtCore, QtWidgets
+from PySide import QtCore, QtWidgets
 
 import FreeCAD
 import FreeCADGui