Fix pylance warning on singleton #12

Job	Run time
build (3.7, pyqt5)	44s
build (3.7, pyqt6)	18s
build (3.7, pyside2)	50s
build (3.7, pyside6)	32s
build (3.8, pyqt5)	46s
build (3.8, pyqt6)	42s
build (3.8, pyside2)	41s
build (3.8, pyside6)	30s
build (3.9, pyqt5)	42s
build (3.9, pyqt6)	42s
build (3.9, pyside2)	47s
build (3.9, pyside6)	28s
build (3.10, pyqt5)	42s
build (3.10, pyqt6)	41s
build (3.10, pyside2)	39s
build (3.10, pyside6)	39s
build (3.11, pyqt5)	38s
build (3.11, pyqt6)	39s
build (3.11, pyside2)	39s
build (3.11, pyside6)	26s
Indicate completion to coveralls.io	0s
	12m 45s

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