Update actions/checkout action to v6 (#378) #3101

Job	Run time
Cache identify	7s
Dependency	4s
Shellcheck	5s
Prepare	8s
Ruff check and force	8s
Check commit	29s
Run pytest using Python 3.13	36s
Run pytest using Python 3.14	33s
Process test coverage	19s
Run mypy	0s
Process test complexity	13s
Build and publish Python 🐍 distributions 📦 to TestPyPI	10s
	2m 52s

Provide feedback