Update actions/checkout action to v7 (#887) #6259

Job	Run time
Cache identify	7s
Dependency	5s
Shellcheck	4s
Prepare	6s
Ruff check and force	10s
Check commit	20s
Run pytest using Python 3.14	21s
Run pytest using Python 3.13	21s
Run mypy	15s
Process test coverage	12s
Build and publish Python 🐍 distributions 📦 to TestPyPI	10s
Process test complexity	9s
	2m 20s

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