Upgrade docsbuild Python to 3.13

[AA-Turner]

d.p.o builds are failing as the server runs Python 3.10, which Sphinx 8.2 has just dropped support for.

[AA-Turner]

Thanks @ewdurbin. The last update (#235) mentioned that we need to update the venvs by hand -- is this still required? If so I'll do so shortly.

A

[ewdurbin]

That's done.

[AA-Turner]

Wonderful, thank you!

[ewdurbin]

the "root" venv described in the state is at least.

ee@docs:~$ sudo /srv/docsbuild/venv/bin/python -V
Python 3.13.2
ee@docs:~$ sudo /srv/docsbuild/venv/bin/python -m pip freeze
certifi==2025.1.31
Jinja2==3.1.5
MarkupSafe==3.0.2
sentry-sdk==2.22.0
setuptools==75.8.0
tomlkit==0.13.2
urllib3==2.3.0
zc.lockfile==3.0.post1

[AA-Turner]

I think the version-specific ones should be rebuilt by dbs.