fix: bump protobuf in /packages/google-cloud-bigquery

Bumps [protobuf](https://github.com/protocolbuffers/protobuf) from 4.25.8 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]

packages/google-cloud-bigquery/testing/constraints-3.10.txt

@@ -24,4 +24,4 @@ opentelemetry-api==1.16.0
 opentelemetry-sdk==1.16.0
 opentelemetry-instrumentation==0.41b0
 proto-plus==1.22.3
-protobuf==4.25.8
+protobuf==5.29.6