test(fix): update the version of protoc such that it supports optiona… (

#1727)

…l label in the .proto file

Thank you for opening a Pull Request! Before submitting your PR, there are a few things you can do to make sure it goes smoothly:
- [ ] Make sure to open an issue as a [bug/issue](https://togithub.com/googleapis/java-bigtable/issues/new/choose) before writing your code!  That way we can discuss the change, evaluate designs, and agree on the general idea
- [ ] Ensure the tests and linter pass
- [ ] Code coverage does not decrease (if any source code was changed)
- [ ] Appropriate docs were updated (if necessary)

Fixes #<issue_number_goes_here> ☕️

If you write sample code, please follow the [samples format](
https://togithub.com/GoogleCloudPlatform/java-docs-samples/blob/main/SAMPLE_FORMAT.md).

test-proxy/pom.xml

@@ -71,7 +71,7 @@
         <artifactId>protobuf-maven-plugin</artifactId>
         <version>0.6.1</version>
         <configuration>
-          <protocArtifact>com.google.protobuf:protoc:3.9.0:exe:${os.detected.classifier}</protocArtifact>
+          <protocArtifact>com.google.protobuf:protoc:3.22.3:exe:${os.detected.classifier}</protocArtifact>
           <pluginId>grpc-java</pluginId>
           <pluginArtifact>io.grpc:protoc-gen-grpc-java:1.24.0:exe:${os.detected.classifier}</pluginArtifact>
         </configuration>