Fix mypy errors (#1486) #1864

Job	Run time
Check code formatting with Black, isort, mypy, flake8 (3.11)	23s
Check that transforms docs are not outdated (3.8)	35s
Test and lint (ubuntu-latest, 3.8)	2m 35s
Test and lint (ubuntu-latest, 3.9)	5m 0s
Test and lint (ubuntu-latest, 3.10)	4m 47s
Test and lint (ubuntu-latest, 3.11)	4m 5s
Test and lint (windows-latest, 3.8)	5m 4s
Test and lint (windows-latest, 3.9)	7m 11s
Test and lint (windows-latest, 3.10)	8m 47s
Test and lint (windows-latest, 3.11)	9m 18s
Test and lint (macos-11, 3.8)	3m 52s
Test and lint (macos-11, 3.9)	6m 5s
Test and lint (macos-11, 3.10)	6m 38s
Test and lint (macos-11, 3.11)	5m 41s
	1h 10m 1s

Provide feedback