Bump @grpc/grpc-js from 1.9.13 to 1.9.15

Bumps [@grpc/grpc-js](https://github.com/grpc/grpc-node) from 1.9.13 to 1.9.15.
- [Release notes](https://github.com/grpc/grpc-node/releases)
- [Commits](https://github.com/grpc/grpc-node/compare/@grpc/grpc-js@1.9.13...@grpc/grpc-js@1.9.15)

---
updated-dependencies:
- dependency-name: "@grpc/grpc-js"
  dependency-type: indirect
...

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