Bump to v1.9.0a0 for testing #5863

Job	Run time
Shellcheck	4s
Cache identify	5s
Dependency	6s
Prepare	1m 17s
Ruff check and force	11s
Check commit	23s
Run pytest using Python 3.13	1m 19s
Run pytest using Python 3.14	38s
Run mypy	14s
Process test coverage	18s
Process test complexity	11s
Build and publish Python 🐍 distributions 📦 to TestPyPI	14s
	5m 0s

Provide feedback