test-selection gap: run single-db tests when there are model changes for CI/Geo

Context

We identified a master-brokentest-selection-gap in gitlab-org/quality/engineering-productivity/master-broken-incidents#362 (closed). It is further discussed in #385168 (comment 1201792093).

Below is a mitigation we discussed:

In the most general sense, I see for now we have CI and Geo for decomposed database. I think it does make sense if we run single-db tests when CI or Geo related features are touched.

However I can see that might be too broad. Maybe we can narrow it down to when there are CI or Geo related model changes, which did happen in https://gitlab.com/gitlab-org/gitlab/-/merge_requests/106213

Goal

Run pipeline:run-single-db jobs when CI/Geo models are changed in an MR.

How to test

• Change a file in app/models/ci/ or app/models/geo/
• Ensure that the single-DB jobs are being run