Keep protobuf-java version consistent

Author: guohao

contrib/pom.xml

@@ -60,7 +60,7 @@
 
         <!-- Dependency Versions -->
         <grpc.version>1.51.0</grpc.version>
-        <protoc.version>3.19.6</protoc.version> <!-- Same version as grpc-proto -->
+        <protoc.version>3.21.9</protoc.version> <!-- Same version as grpc-proto -->
         <slf4j.version>2.0.5</slf4j.version>
         <gson.version>2.10</gson.version> <!-- Same version as grpc-proto -->
         <mustache-java.version>0.9.10</mustache-java.version>