chore: update required checks

[tswast]

In https://github.com/googleapis/python-bigquery-magics/pull/7, I commented out several required checks. We should add these back in https://github.com/googleapis/python-bigquery-magics/blob/main/.github/sync-repo-settings.yaml

Some notes:

• Samples: blocked by https://github.com/googleapis/python-bigquery-magics/pull/9
• "Kokoro": maybe redundant with system tests and/or unit tests and linting. We may want to drop that in favor of the smaller test jobs.

[tswast]

Re-opening so that we require:

• Kokoro system-3.12
• samples once we have those

[tswast]

Samples have been merged in https://github.com/googleapis/python-bigquery-magics/pull/9

We can add at least one samples tests to the required checks.