Pin all Qt bindings for minimum version CI

Author: QuLogic

.github/workflows/tests.yml

@@ -37,6 +37,9 @@ jobs:
             python-version: 3.8
             extra-requirements: '-c requirements/testing/minver.txt'
             pyqt5-ver: '==5.11.2 sip==5.0.0'  # oldest versions with a Py3.8 wheel.
+            pyqt6-ver: '==6.1.0 PyQt6-Qt6==6.1.0'
+            pyside2-ver: '==5.14.0'  # oldest version with working Py3.8 wheel.
+            pyside6-ver: '==6.0.0'
             delete-font-cache: true
           - os: ubuntu-20.04
             python-version: 3.8
@@ -189,17 +192,17 @@ jobs:
             echo 'PyQt5 is available' ||
             echo 'PyQt5 is not available'
           if [[ "${{ runner.os }}" != 'macOS' ]]; then
-            python -mpip install --upgrade pyside2 &&
+            python -mpip install --upgrade pyside2${{ matrix.pyside2-ver }} &&
               python -c 'import PySide2.QtCore' &&
               echo 'PySide2 is available' ||
               echo 'PySide2 is not available'
           fi
           if [[ "${{ matrix.os }}" = ubuntu-20.04 ]]; then
-            python -mpip install --upgrade pyqt6 &&
+            python -mpip install --upgrade pyqt6${{ matrix.pyqt6-ver }} &&
               python -c 'import PyQt6.QtCore' &&
               echo 'PyQt6 is available' ||
               echo 'PyQt6 is not available'
-            python -mpip install --upgrade pyside6 &&
+            python -mpip install --upgrade pyside6${{ matrix.pyside6-ver }} &&
               python -c 'import PySide6.QtCore' &&
               echo 'PySide6 is available' ||
               echo 'PySide6 is not available'

lib/matplotlib/backends/qt_compat.py

@@ -92,7 +92,10 @@ def _isdeleted(obj): return not shiboken6.isValid(obj)
         _isdeleted = sip.isdeleted
     elif QT_API == QT_API_PYSIDE2:
         from PySide2 import QtCore, QtGui, QtWidgets, __version__
-        import shiboken2
+        try:
+            from PySide2 import shiboken2
+        except ImportError:
+            import shiboken2
         def _isdeleted(obj):
             return not shiboken2.isValid(obj)
     else: