bump testpypi to a6 #2616

Job	Run time
Shellcheck	5s
Dependency	5s
Cache identify	7s
Prepare	9s
Ruff check and force	12s
Check commit	30s
Run pytest using Python 3.13	34s
Process test coverage	13s
Run mypy	-1s
Process test complexity	12s
Build and publish Python 🐍 distributions 📦 to TestPyPI	11s
	2m 17s

Provide feedback