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

What does this MR do and why?

Contributes to #482942 (closed)

Problem

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

• Optimize: association loading for RepositoryCon... (!169280 - merged)
• Optimization: don't load group if not needed (!169276 - merged)
• Optimization: don't load a User when user_id is... (!169163 - merged)

Solution

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