Bump protobuf in /examples/reservations-bot-demo/cloud_function

Bumps [protobuf](https://github.com/protocolbuffers/protobuf) from 3.18.3 to 4.25.8.
- [Release notes](https://github.com/protocolbuffers/protobuf/releases)
- [Changelog](https://github.com/protocolbuffers/protobuf/blob/main/protobuf_release.bzl)
- [Commits](protocolbuffers/protobuf@v3.18.3...v4.25.8)

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

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

Author: dependabot[bot]

examples/reservations-bot-demo/cloud_function/requirements.txt

@@ -6,7 +6,7 @@ enum-compat==0.0.3
 googleapis-common-protos==1.52.0
 grpcio==1.53.2
 idna==2.10
-protobuf==3.18.3
+protobuf==4.25.8
 pycparser==2.20
 pydantic==1.6.2
 PyJWT==2.4.0