[post-migration] test review

### Summary of the issue

During the migration certain issues arose with ensuring the presubmit tests passed. Review the libraries to confirm whether tests marked `skip` (i.e. due to environmental issues OR dependency version issues) should be updated OR left marked as `skip`.

**sqlalchemy-bigquery**
Double check the extra test skipped in #16046 via this commit: https://github.com/googleapis/google-cloud-python/pull/16046/commits/05d45fcb49ba05e1a54e8c7d688fd780baf1f013

UPDATE (20260511: resolved in #15506)
**python-bigquery**
See this commit from #16008 as an example: https://github.com/googleapis/google-cloud-python/pull/16008/commits/7e206e590d741f13d9ee96b6b9b05ccaaf6d4af5

Specifically the 7 test marked as skipped here:
```
........................................................................ [ 37%]
.................................ss...........sssss..................... [ 75%]
.............................................. [100%]
183 passed, 7 skipped in 350.52s (0:05:50)
```

We may want to audit skipped tests in all packages as well

Review the skipped tests in sqlalchemy-bigquery, starting with the extra skip added in #16046 and commit 05d45fcb. Check the seven skipped python-bigquery tests against #16008 and commit 7e206e590d741f13d9ee96b6b9b05ccaaf6d4af5; the work is done when each skip is either justified or updated, with the broader package audit considered.

Escrito por el modelo de indexación a partir del texto del issue.