ci: Update renovate to track Arch Linux repos using repology

[dylanmtaylor]

Pin runtime deps to current Arch package versions and configure Renovate to use the Repology datasource (Arch repos) instead of PyPI for version bumps. This prevents mismatches like #4427 where a PyPI release landed before Arch shipped it. Dev deps stay on PyPI since they only run in CI.

[dylanmtaylor]

One consideration, repology scrapes the versions from Arch packages, but might slightly lag - in practice this means the PR would be opened a bit later. Probably irrelevant but worth pointing out.

[codefiles]

Did you consider any of the other datasources?

https://docs.renovatebot.com/modules/datasource/git-tags/
https://docs.renovatebot.com/modules/datasource/gitlab-tags/
https://gitlab.archlinux.org/archlinux/packaging/packages/python-pydantic/-/tags

[dylanmtaylor]

Did you consider any of the other datasources?

https://docs.renovatebot.com/modules/datasource/git-tags/
https://docs.renovatebot.com/modules/datasource/gitlab-tags/
https://gitlab.archlinux.org/archlinux/packaging/packages/python-pydantic/-/tags

I picked repology because I'm familiar with it from my work on some NixOS packages. I suspect that repology will work well for us.

[codefiles]

I will submit a pull request to query the version information from Arch Linux channels rather than Repology then. Is that ok with you?

[dylanmtaylor]

That's fine