Fix ClassCanBeStatic warnings

When all error prone warnings are enabled a number of ClassCanBeStatic
bug patterns is reported:

[1] https://errorprone.info/bugpattern/ClassCanBeStatic

Change-Id: I6dfcf9cf03db7001c8ca0f2811cdaa9823d942ea

src/test/java/com/googlesource/gerrit/plugins/multisite/broker/kafka/BrokerPublisherTest.java

diff --git a/src/test/java/com/googlesource/gerrit/plugins/multisite/broker/kafka/BrokerPublisherTest.java b/src/test/java/com/googlesource/gerrit/plugins/multisite/broker/kafka/BrokerPublisherTest.java
index fe73065..8131a3f 100644
--- a/src/test/java/com/googlesource/gerrit/plugins/multisite/broker/kafka/BrokerPublisherTest.java
+++ b/src/test/java/com/googlesource/gerrit/plugins/multisite/broker/kafka/BrokerPublisherTest.java
@@ -140,7 +140,7 @@
     assertThat(publisher.eventToJson(event).equals(expectedCommentEventJsonObject)).isTrue();
   }
 
-  private class TestBrokerSession implements BrokerSession {
+  private static class TestBrokerSession implements BrokerSession {
 
     @Override
     public boolean isOpen() {

src/test/java/com/googlesource/gerrit/plugins/multisite/kafka/consumer/EventConsumerIT.java

diff --git a/src/test/java/com/googlesource/gerrit/plugins/multisite/kafka/consumer/EventConsumerIT.java b/src/test/java/com/googlesource/gerrit/plugins/multisite/kafka/consumer/EventConsumerIT.java
index 3e8b3ca..2cc7c16 100644
--- a/src/test/java/com/googlesource/gerrit/plugins/multisite/kafka/consumer/EventConsumerIT.java
+++ b/src/test/java/com/googlesource/gerrit/plugins/multisite/kafka/consumer/EventConsumerIT.java
@@ -75,7 +75,7 @@
 
   public static class KafkaTestContainerModule extends LifecycleModule {
 
-    public class KafkaStopAtShutdown implements LifecycleListener {
+    public static class KafkaStopAtShutdown implements LifecycleListener {
       private final KafkaContainer kafka;
 
       public KafkaStopAtShutdown(KafkaContainer kafka) {