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_workers_installation.py

@@ -34,7 +34,7 @@ import zipfile
 from typing import Dict, List
 from enum import Enum, auto
 
-from PySide2 import QtCore
+from PySide import QtCore
 
 import FreeCAD
 import addonmanager_utilities as utils