feat(spanner): [Spanner] isolation_level and read_lock_mode are added to message .google.spanner.v1.CommitResponse (#9140)

* feat(spanner): `isolation_level` and `read_lock_mode` are added to message `.google.spanner.v1.CommitResponse`

PiperOrigin-RevId: 906456285

Source-Link: googleapis/googleapis@a7f4ee2

Source-Link: googleapis/googleapis-gen@70ae95e
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* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

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Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

Author: gcf-owl-bot[bot]