**Backport:** https://codeberg.org/forgejo/forgejo/pulls/8681
- If a repository only has the 'manual merge' strategy allowed, the mergebox should still be shown.
- The condition that checks if all merge strategies are disabled didn't check for the manual merge strategy.
- Add a integration test that demonstrates this fix is effective.
Reported-by: apteryx
Co-authored-by: Gusted <postmaster@gusted.xyz>
Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/8683
Reviewed-by: Earl Warren <earl-warren@noreply.codeberg.org>
Co-authored-by: forgejo-backport-action <forgejo-backport-action@noreply.codeberg.org>
Co-committed-by: forgejo-backport-action <forgejo-backport-action@noreply.codeberg.org>
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