bump testpypi to a6 #2614

Job	Run time
Cache identify	4s
Shellcheck	5s
Dependency	3s
Prepare	1m 21s
Ruff check and force	11s
Check commit	33s
Run pytest using Python 3.13	1m 33s
Process test coverage	20s
Run mypy	-1s
Process test complexity	10s
Build and publish Python 🐍 distributions 📦 to TestPyPI	12s
	4m 31s

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