chore: Add BigQuery Dataframes team to CODEOWNERS (#16585)

This adds the `@googleapis/bigquery-dataframe-team` to the `CODEOWNERS`
file for all BigQuery-related packages under the `packages/` directory,
specifically ensuring that connector packages like `pandas-gbq`,
`sqlalchemy-bigquery`, and `bigquery-magics` are included. Existing
owners (`@googleapis/cloud-sdk-python-team` and
`@googleapis/cloud-sdk-librarian-team`) have been retained for these
paths.

---
*PR created automatically by Jules for task
[4709133254732906551](https://jules.google.com/task/4709133254732906551)
started by @tswast*

---------

Co-authored-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>
Co-authored-by: tswast <247555+tswast@users.noreply.github.com>

Author: tswast

.github/CODEOWNERS

@@ -12,6 +12,10 @@
 *                                             @googleapis/cloud-sdk-python-team @googleapis/cloud-sdk-librarian-team
 
 /packages/bigframes/                          @googleapis/cloud-sdk-python-team @googleapis/cloud-sdk-librarian-team @googleapis/bigquery-dataframe-team
+/packages/bigquery-magics/                    @googleapis/cloud-sdk-python-team @googleapis/cloud-sdk-librarian-team @googleapis/bigquery-dataframe-team
 /packages/django-google-spanner/              @googleapis/cloud-sdk-python-team @googleapis/cloud-sdk-librarian-team @googleapis/spanner-team
 /packages/google-auth/                        @googleapis/cloud-sdk-python-team @googleapis/cloud-sdk-librarian-team @googleapis/cloud-sdk-auth-team @googleapis/aion-team
+/packages/google-cloud-bigquery*/             @googleapis/cloud-sdk-python-team @googleapis/cloud-sdk-librarian-team @googleapis/bigquery-dataframe-team
 /packages/google-cloud-spanner/               @googleapis/cloud-sdk-python-team @googleapis/cloud-sdk-librarian-team @googleapis/spanner-team
+/packages/pandas-gbq/                         @googleapis/cloud-sdk-python-team @googleapis/cloud-sdk-librarian-team @googleapis/bigquery-dataframe-team
+/packages/sqlalchemy-bigquery/                @googleapis/cloud-sdk-python-team @googleapis/cloud-sdk-librarian-team @googleapis/bigquery-dataframe-team