Bump protobuf-java from 3.12.2 to 3.16.1 in /metadata (#2715)

Bumps [protobuf-java](https://github.com/protocolbuffers/protobuf) from 3.12.2 to 3.16.1.
- [Release notes](https://github.com/protocolbuffers/protobuf/releases)
- [Changelog](https://github.com/protocolbuffers/protobuf/blob/master/generate_changelog.py)
- [Commits](https://github.com/protocolbuffers/protobuf/compare/v3.12.2...v3.16.1)

---
updated-dependencies:
- dependency-name: com.google.protobuf:protobuf-java
  dependency-type: direct:production
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Tijana Vislavski Gradina <tijanavg@google.com>

metadata/pom.xml

@@ -108,7 +108,7 @@
     <dependency>
       <groupId>com.google.protobuf</groupId>
       <artifactId>protobuf-java</artifactId>
-      <version>3.12.2</version>
+      <version>3.16.1</version>
     </dependency>
 
     <!-- https://mvnrepository.com/artifact/com.google.auto.value/auto-value -->