1.5.0 - QGIS4 support

What's Changed

• Print a warning when the relations are invalid by @domi4484 in #51
• Prepare for Qt6 and QGIS4 by @merydian in #55
• Add missing PyQt6 preparations by @merydian in #57
• Add pyqt6-check job to actions workflow by @merydian in #56

New Contributors

• @merydian made their first contribution in #55

Full Changelog: v1.4.0...v1.5.0