Update actions/checkout action to v6.0.3 (#451) #3452

Job	Run time
Cache identify	7s
Dependency	4s
Shellcheck	5s
Prepare	9s
Ruff check and force	6s
Check commit	35s
Run pytest using Python 3.14	33s
Process test coverage	10s
Run mypy	0s
Process test complexity	6s
Build and publish Python 🐍 distributions 📦 to TestPyPI	8s
	2m 3s

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