This PR is part of https://codeberg.org/forgejo/forgejo/pulls/4767 filed by @algernon
Validateable is enhanced for less duplication.
## Checklist
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### Tests
- I added test coverage for Go changes...
- [x] in their respective `*_test.go` for unit tests.
### Release notes
- [x] I do not want this change to show in the release notes.
- [ ] I want the title to show in the release notes with a link to this pull request.
- [ ] I want the content of the `release-notes/<pull request number>.md` to be be used for the release notes instead of the title.
Co-authored-by: zam <mirco.zachmann@meissa.de>
Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/7714
Reviewed-by: Earl Warren <earl-warren@noreply.codeberg.org>
Co-authored-by: Michael Jerger <michael.jerger@meissa-gmbh.de>
Co-committed-by: Michael Jerger <michael.jerger@meissa-gmbh.de>