Bump @grpc/grpc-js from 1.9.13 to 1.9.15 (#1573)

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/[email protected]...@grpc/[email protected])

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

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Daniel Lee <[email protected]>