Use github-refs for GitHub Actions so that branches are supported in addition to tags

[rarkins]

Describe the proposed change(s).

In GitHub Actions, and also likely some other managers such as npm, references to GitHub are not limited to only tags but also branches. In shorthand this is known as "references".

We need a new datasource called github-refs which fetches git refs - including branch names - and then enriches it with tags and releases data.

After that we need to check all managers which currently reference github-tags or github-releases and see if github-refs is better.

Reproduction repo: https://github.com/renovate-reproductions/28016

[karlhorky]

This would also enable support for pnpm/action-setup, which is currently not updated with the @v2, @v3 etc version recommended in the readme:

• pnpm/setup-action not updated #29245

[rarkins]

Here's an example public repository refs Rest API which has a branch we're interested in (v1): https://api.github.com/repos/oracle-actions/setup-java/git/refs?per_page=100

The per_page parameter seems to work (increasing from default 30 to 100) but I haven't found a way to get them to sort by date (and nor do they include date in their response). This would would mean we have the need to fetch every page every time, to make sure our results include the latest.

This lack of (a) timestamps and (b) sorting is why we still use the GraphQL API for github-tags and github-releases datasources, so we may need to do so again here.