**Backport:** https://codeberg.org/forgejo/forgejo/pulls/13406
Forgejo only added the legacy `gitea_default_actions_url`.
### Tests for Go changes
- I added test coverage for Go changes...
- [x] in their respective `*_test.go` for unit tests.
- [ ] in the `tests/integration` directory if it involves interactions with a live Forgejo server.
- I ran...
- [x] `make pr-go` before pushing
### Release notes
- [ ] This change will be noticed by a Forgejo user or admin (feature, bug fix, performance, etc.). I suggest to include a release note for this change.
- [x] This change is not visible to a Forgejo user or admin (refactor, dependency upgrade, etc.). I think there is no need to add a release note for this change.
Co-authored-by: Andreas Ahlenstorf <andreas@ahlenstorf.ch>
Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/13411
Reviewed-by: Mathieu Fenniak <mfenniak@noreply.codeberg.org>
