build(deps): bump protobuf-gradle-plugin from 0.8.19 to 0.9.1

Bumps [protobuf-gradle-plugin](https://github.com/google/protobuf-gradle-plugin) from 0.8.19 to 0.9.1.
- [Release notes](https://github.com/google/protobuf-gradle-plugin/releases)
- [Commits](google/protobuf-gradle-plugin@v0.8.19...0.9.1)

---
updated-dependencies:
- dependency-name: com.google.protobuf:protobuf-gradle-plugin
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

build.gradle

@@ -28,7 +28,7 @@ buildscript {
         classpath "org.jetbrains.dokka:dokka-gradle-plugin:${version_dokka}"
         // NOTE: Do not place your application dependencies here; they belong
         // in the individual module build.gradle files
-        classpath 'com.google.protobuf:protobuf-gradle-plugin:0.8.19'
+        classpath 'com.google.protobuf:protobuf-gradle-plugin:0.9.1'
 
         classpath 'gradle.plugin.org.mozilla.rust-android-gradle:plugin:0.9.0'