Marked exactly_one_of for cloudbuild trigger repoSource tag/branch/commit

[modular-magician]

Related to #9936

It looks like exactly_one_of was missing for the branch/tag/commit, so you could skip adding one of them, which is incorrect. This change should bring the behavior in line with the REST API documentation.

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cloudbuild: marked `google_cloudbuild_trigger` as requiring one of branch_name/tag_name/commit_sha  within build.source.repo_source

Derived from GoogleCloudPlatform/magic-modules#5155

[github-actions]

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