Bump grpcio from 1.47.0 to 1.48.1 in /docker (#12201)

Bumps [grpcio](https://github.com/grpc/grpc) from 1.47.0 to 1.48.1.
- [Release notes](https://github.com/grpc/grpc/releases)
- [Changelog](https://github.com/grpc/grpc/blob/master/doc/grpc_release_schedule.md)
- [Commits](grpc/grpc@v1.47.0...v1.48.1)

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

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docker/linux-pinned-requirements.txt

@@ -173,7 +173,7 @@ greenlet==1.1.2
     # via gevent
 grpc-google-iam-v1==0.12.4
     # via google-cloud-logging
-grpcio==1.47.0
+grpcio==1.48.1
     # via
     #   google-api-core
     #   googleapis-common-protos