chore: Update gapic-generator-python to v1.16.1 (#279)

* chore: Update gapic-generator-python to v1.16.1

PiperOrigin-RevId: 618243632

Source-Link: googleapis/googleapis@078a38b

Source-Link: googleapis/googleapis-gen@7af768c
Copy-Tag: eyJwIjoiLmdpdGh1Yi8uT3dsQm90LnlhbWwiLCJoIjoiN2FmNzY4YzNmOGNlNTg5OTQ0ODIzNTBmNzQwMTE3MzMyOTk1MGEzMSJ9

* 🦉 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>