Related to #2773
Related to Refactor URL detection [gitea#29960](https://github.com/go-gitea/gitea/pull/29960)
Related to Refactor external URL detection [gitea#29973](https://github.com/go-gitea/gitea/pull/29973)
I added a bunch of tests to `httplib.TestIsRiskyRedirectURL` and some cases should be better handled (however it is not an easy task).
I also ported the removal of `utils.IsExternalURL`, since it prevents duplicated (subtle) code.
Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/3167
Reviewed-by: Earl Warren <earl-warren@noreply.codeberg.org>
Reviewed-by: Gusted <gusted@noreply.codeberg.org>
Co-authored-by: oliverpool <git@olivier.pfad.fr>
Co-committed-by: oliverpool <git@olivier.pfad.fr>
16879b07d2