PR: Add `QtCore.Qt.MouseButton.MidButton` alias for Qt6 #1093

Job	Run time
Test ubuntu-latest Python 3.7 conda=Yes	3m 29s
Test ubuntu-latest Python 3.7 conda=No	3m 38s
Test ubuntu-latest Python 3.11 conda=Yes	2m 39s
Test ubuntu-latest Python 3.11 conda=No	2m 39s
Test windows-latest Python 3.7 conda=Yes	6m 1s
Test windows-latest Python 3.7 conda=No	6m 23s
Test windows-latest Python 3.11 conda=Yes	7m 45s
Test windows-latest Python 3.11 conda=No	6m 42s
Test macos-13 Python 3.7 conda=Yes	5m 36s
Test macos-13 Python 3.7 conda=No	8m 39s
Test macos-13 Python 3.11 conda=Yes	7m 0s
Test macos-13 Python 3.11 conda=No	12m 39s
Finish Coveralls	5s
	1h 13m 15s

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