Support merge_group webhooks fired by merge queues. PR created based on #1316

Author: felipefrancisco

src/main/java/org/kohsuke/github/GHEvent.java

@@ -102,6 +102,9 @@ public enum GHEvent {
     /** The merge queue entry. */
     MERGE_QUEUE_ENTRY,
 
+    /** The merge group entry. */
+    MERGE_GROUP,
+
     /** The meta. */
     META,
 

src/test/java/org/kohsuke/github/EnumTest.java

@@ -32,7 +32,7 @@ public void touchEnums() {
 
         assertThat(GHDirection.values().length, equalTo(2));
 
-        assertThat(GHEvent.values().length, equalTo(64));
+        assertThat(GHEvent.values().length, equalTo(65));
         assertThat(GHEvent.ALL.symbol(), equalTo("*"));
         assertThat(GHEvent.PULL_REQUEST.symbol(), equalTo(GHEvent.PULL_REQUEST.toString().toLowerCase()));