deps: update dependency com.google.protobuf:protobuf-java to v3.12.2

Author: renovate-bot

pom.xml

@@ -68,7 +68,7 @@
  <google.common-protos.version>1.18.0</google.common-protos.version>
  <gax.version>1.56.0</gax.version>
  <grpc.version>1.30.0</grpc.version>
- <protobuf.version>3.12.0</protobuf.version>
+ <protobuf.version>3.12.2</protobuf.version>
  <junit.version>4.13</junit.version>
  <guava.version>29.0-android</guava.version>
  <threeten.version>1.4.4</threeten.version>