Move to anndata 0.11

[tcompa]

0.11.0rc1 is available for testing (https://pypi.org/project/anndata/0.11.0rc1)

Release notes are at https://github.com/scverse/anndata/blob/main/docs/release-notes/0.11.0rc1.md, and they include

Export {func}~anndata.write_elem and {func}~anndata.read_elem directly from the main package instead of experimental {user}ilan-gold ({pr}1598)

[tcompa]

0.11 has now been released, ref https://anndata.readthedocs.io/en/latest/release-notes/index.html#v0-11-0

[jluethi]

They drop Python 3.9 support in that. So let's make sure we update that when we also drop Python 3.9 support. (also needed for ngio anyhow)