Remove unnecessary `mypy` check in CI #55

Job	Run time
test (windows-latest, 3.14, muse2_windows.zip, muse2.exe)	58s
test (ubuntu-latest, 3.14, muse2_linux.tar.gz, muse2)	29s
test (macos-latest, 3.14, muse2_macos_arm.tar.gz, muse2)	43s
	2m 10s

Provide feedback