Bump protobuf from 6.30.2 to 6.31.1 in /tests

Bumps [protobuf](https://github.com/protocolbuffers/protobuf) from 6.30.2 to 6.31.1.
- [Release notes](https://github.com/protocolbuffers/protobuf/releases)
- [Changelog](https://github.com/protocolbuffers/protobuf/blob/main/protobuf_release.bzl)
- [Commits](protocolbuffers/protobuf@v6.30.2...v6.31.1)

---
updated-dependencies:
- dependency-name: protobuf
  dependency-version: 6.31.1
  dependency-type: indirect
...

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Author: dependabot[bot]