chore: unify cascade-setup-forgejo with cascade-forgejo (#919)

Tested out of the wip-cascade branch:

- https://code.forgejo.org/forgejo/runner/actions/runs/8746
- https://code.forgejo.org/actions/setup-forgejo/pulls/646
- https://code.forgejo.org/forgejo/end-to-end/pulls/984

----

Instead of always running end-to-end tests, only run them when the
run-end-to-end-tests label is set. They are heavy duty and should not
be run when a new contributor sends their first pull request.

- fix bug: close-merge is close
- add instructions for debug
- identify the origin of the tokens
- do not needlessly run setup-forgejo integration tests
- copy/paste from cascade-forgejo.yml with the following exceptions:
  - do not trigger on main
  - use run-end-to-end-test instead of run-forgejo-test

<!--start release-notes-assistant-->
<!--URL:https://code.forgejo.org/forgejo/runner-->
- other
  - [PR](https://code.forgejo.org/forgejo/runner/pulls/919): <!--number 919 --><!--line 0 --><!--description Y2hvcmU6IHVuaWZ5IGNhc2NhZGUtc2V0dXAtZm9yZ2VqbyB3aXRoIGNhc2NhZGUtZm9yZ2Vqbw==-->chore: unify cascade-setup-forgejo with cascade-forgejo<!--description-->
<!--end release-notes-assistant-->

Reviewed-on: https://code.forgejo.org/forgejo/runner/pulls/919
Reviewed-by: Mathieu Fenniak <mfenniak@noreply.code.forgejo.org>
Co-authored-by: Earl Warren <contact@earl-warren.org>
Co-committed-by: Earl Warren <contact@earl-warren.org>

renovate.json

@@ -9,6 +9,6 @@
       "separateMinorPatch": true
     }
   ],
-  "labels": ["Kind/Chore"],
+  "labels": ["Kind/Chore", "run-end-to-end-tests"],
   "ignorePaths": ["**/testdata/**", "**/node_modules/**"]
 }