Bump protobuf.version from 3.21.5 to 3.21.6 (#542)

Bumps `protobuf.version` from 3.21.5 to 3.21.6.

Updates `protobuf-java` from 3.21.5 to 3.21.6
- [Release notes](https://github.com/protocolbuffers/protobuf/releases)
- [Changelog](https://github.com/protocolbuffers/protobuf/blob/main/generate_changelog.py)
- [Commits](protocolbuffers/protobuf@v3.21.5...v3.21.6)

Updates `protobuf-java-util` from 3.21.5 to 3.21.6

---
updated-dependencies:
- dependency-name: com.google.protobuf:protobuf-java
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: com.google.protobuf:protobuf-java-util
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

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

pom.xml

@@ -51,7 +51,7 @@
     <!-- https://spring.io/projects/spring-cloud#release-trains -->
     <spring-cloud.version>2021.0.4</spring-cloud.version>
     <spring-retry.version>1.3.3</spring-retry.version>
-    <protobuf.version>3.21.5</protobuf.version>
+    <protobuf.version>3.21.6</protobuf.version>
     <json-simple.version>1.1.1</json-simple.version>
     <jackson.version>2.13.4</jackson.version>
     <log4j.version>2.18.0</log4j.version>