Merge pull request #1587 from kubernetes-client/dependabot/maven/com.google.protobuf-protobuf-java-3.15.6

Bump protobuf-java from 3.15.5 to 3.15.6

Author: k8s-ci-robot

pom.xml

@@ -43,7 +43,7 @@
     <snakeyaml.version>1.28</snakeyaml.version>
     <slf4j.version>1.7.30</slf4j.version>
     <caffeine.version>2.9.0</caffeine.version>
-    <protobuf.version>3.15.5</protobuf.version>
+    <protobuf.version>3.15.6</protobuf.version>
     <junit.version>4.13</junit.version>
     <bucket4j.version>6.0.1</bucket4j.version>
     <bouncycastle.version>1.68</bouncycastle.version>