deps: reverting protobuf to 3.19.4 (#657)

Author: suztomo

java-shared-dependencies/first-party-dependencies/pom.xml

@@ -59,7 +59,7 @@
     <gax.version>2.16.0</gax.version>
     <grpc-gcp.version>1.1.0</grpc-gcp.version>
     <guava.version>31.1-jre</guava.version>
-    <protobuf.version>3.20.0</protobuf.version>
+    <protobuf.version>3.19.4</protobuf.version>
     <google.api-common.version>2.1.5</google.api-common.version>
     <google.common-protos.version>2.8.3</google.common-protos.version>
     <google.core.version>2.5.11</google.core.version>