use aqt.qt to (partially) mock the old PyQt5 module

We can't import the Qt5 libraries to do it - they are not usually
available, and it will lead to crashes if both are imported at once.

qt/aqt/qt/compat.py

@@ -1256,10 +1256,9 @@ QDBus.AutoDetect = QDBus.CallMode.AutoDetect
 QHostAddress.LocalHost = QHostAddress.SpecialAddress.LocalHost
 QPrinter.Millimeter = QPrinter.Unit.Millimeter
 
-# Globally alias removed PyQt5.Qt to PyQt6.QtCore.Qt
+# Mock the removed PyQt5.Qt module
 ##########################################################################
 
 from . import qt5qt
 
 sys.modules["PyQt5.Qt"] = qt5qt
-sys.modules["PyQt6.Qt"] = qt5qt

qt/aqt/qt/qt5qt.py

@@ -1,7 +1,6 @@
 # Copyright: Ankitects Pty Ltd and contributors
 # License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
 
-# make sure not to optimize imports on this file
 # pylint: skip-file
 
 """
@@ -10,8 +9,8 @@ Compatibility shim for PyQt5.Qt
 
 from typing import Any
 
-from .qt5 import *
-
 
 def __getattr__(name: str) -> Any:
-    return getattr(Qt, name)  # type: ignore
+    import aqt.qt
+
+    return getattr(aqt.qt, name)