Add support for GitHub event branch_protection_rule

Author: gjabouley-invn

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

@@ -10,6 +10,7 @@
  * @see <a href="https://developer.github.com/v3/activity/events/types/">Event type reference</a>
  */
 public enum GHEvent {
+    BRANCH_PROTECTION_RULE,
     CHECK_RUN,
     CHECK_SUITE,
     CODE_SCANNING_ALERT,

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

@@ -28,7 +28,7 @@ public void touchEnums() {
 
         assertThat(GHDirection.values().length, equalTo(2));
 
-        assertThat(GHEvent.values().length, equalTo(62));
+        assertThat(GHEvent.values().length, equalTo(63));
         assertThat(GHEvent.ALL.symbol(), equalTo("*"));
         assertThat(GHEvent.PULL_REQUEST.symbol(), equalTo(GHEvent.PULL_REQUEST.toString().toLowerCase()));