Projects::Settings::RepositoryController#show: re-enable query limit

Contributes to https://gitlab.com/gitlab-org/gitlab/-/issues/482942

**Problem**

The endpoint executed more than 100 queries in the past. After several
optimizations it should be possible to re-enable the limit.

**Solution**

* Re-enable the query limit
* Ensure that the limit is below 100 in tests.

Changelog: other