Add fastAPI test coverage for `upstream_map_indexes` in execution API

[amoghrajesh]

Body

#49996 added support for returning upstream_map_indexes as response of the /run endpoint but there is no test coverage that checks if expected value is returned or not.

We should ideally cover it so that any regressions are caught.

Committer

• I acknowledge that I am a maintainer/committer of the Apache Airflow project.

[anasatzemoso]

Can I work on this issue ?

[anasatzemoso]

I looked into this and found that there’s already a parameterized test (test_ti_run) for the /execution/task-instances/{ti.id}/run endpoint. It patches _get_upstream_map_indexes and asserts that the upstream_map_indexes field is returned in the response with the expected structure across multiple scenarios (ints, lists, None, mixed types).

This seems to cover the gap mentioned in the issue — verifying that the field is returned correctly in the API response. Could you confirm if this is the intended scope, or if there’s anything additional expected here?