Fixes#12937.
The intent of this change is to allow Forgejo to evaluate `if` without having to send jobs to a runner. When you send a job to a runner just for it to return "skipped!", it takes up 1 runner capacity for a `fetch_interval` period, which can be avoided if Forgejo can evaluate the `if` condition itself.
### Tests for Go changes
- I added test coverage for Go changes...
- [x] in their respective `*_test.go` for unit tests.
- [x] in the `tests/integration` directory if it involves interactions with a live Forgejo server.
- I ran...
- [x] `make pr-go` before pushing
### Documentation
- [ ] I created a pull request [to the documentation](https://codeberg.org/forgejo/docs) to explain to Forgejo users how to use this change.
- [x] I did not document these changes and I do not expect someone else to do it.
### Release notes
- [x] 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.
- [ ] 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.
Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/13030
Reviewed-by: Andreas Ahlenstorf <aahlenst@noreply.codeberg.org>
6b3359f016