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

Bumps [protobuf](https://github.com/protocolbuffers/protobuf) from 4.21.12 to 5.29.6.
- [Release notes](https://github.com/protocolbuffers/protobuf/releases)
- [Commits](https://github.com/protocolbuffers/protobuf/commits)

---
updated-dependencies:
- dependency-name: protobuf
  dependency-version: 5.29.6
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

chat/client-libraries/cloud/requirements.txt

@@ -1,3 +1,3 @@
 google_auth_oauthlib==1.2.0
-protobuf==4.21.12
+protobuf==5.29.6
 google-apps-chat==0.1.9