fix: Allow Protobuf 6.x (googleapis#13651)

- [ ] Regenerate this pull request now.

PiperOrigin-RevId: 736168602

Source-Link:
googleapis/googleapis@1f01eef

Source-Link:
https://github.com/googleapis/googleapis-gen/commit/e687c8953cf088e4b39397e33af6e2238e1720aa
Copy-Tag:
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