Bump grpcio from 1.75.1 to 1.78.0

Bumps [grpcio](https://github.com/grpc/grpc) from 1.75.1 to 1.78.0.
- [Release notes](https://github.com/grpc/grpc/releases)
- [Commits](grpc/grpc@v1.75.1...v1.78.0)

---
updated-dependencies:
- dependency-name: grpcio
  dependency-version: 1.78.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

requirements/extras/gcpubsub.txt

@@ -1,4 +1,4 @@
 google-cloud-pubsub>=2.18.4
 google-cloud-monitoring>=2.16.0
-grpcio==1.76.0
+grpcio==1.78.0
 protobuf==6.33.5