build(deps): bump protobuf in /chat/client-libraries/cloud

Bumps [protobuf](https://github.com/protocolbuffers/protobuf) from 4.21.12 to 4.25.8.
- [Release notes](https://github.com/protocolbuffers/protobuf/releases)
- [Changelog](https://github.com/protocolbuffers/protobuf/blob/main/protobuf_release.bzl)
- [Commits](https://github.com/protocolbuffers/protobuf/commits/v4.25.8)

---
updated-dependencies:
- dependency-name: protobuf
  dependency-version: 4.25.8
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

chat/client-libraries/cloud/requirements.txt

@@ -1,3 +1,3 @@
 google_auth_oauthlib==1.2.0
-protobuf==4.21.12
+protobuf==4.25.8
 google-apps-chat==0.1.9