Bump com.google.api.grpc:proto-google-iam-v1 in /plugins/repository-gcs

Bumps [com.google.api.grpc:proto-google-iam-v1](https://github.com/googleapis/sdk-platform-java) from 0.12.0 to 1.20.0.
- [Release notes](https://github.com/googleapis/sdk-platform-java/releases)
- [Changelog](https://github.com/googleapis/sdk-platform-java/blob/main/CHANGELOG.md)
- [Commits](https://github.com/googleapis/sdk-platform-java/commits)

---
updated-dependencies:
- dependency-name: com.google.api.grpc:proto-google-iam-v1
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

plugins/repository-gcs/build.gradle

@@ -61,7 +61,7 @@ dependencies {
   api 'com.google.api-client:google-api-client:2.2.0'
 
   api 'com.google.api.grpc:proto-google-common-protos:2.10.0'
-  api 'com.google.api.grpc:proto-google-iam-v1:0.12.0'
+  api 'com.google.api.grpc:proto-google-iam-v1:1.20.0'
 
   api "com.google.auth:google-auth-library-credentials:${versions.google_auth}"
   api "com.google.auth:google-auth-library-oauth2-http:${versions.google_auth}"