Make class DraftChangeIT.MarkChangeAsDraftUpdateOp static

Otherwise ErrorProne complains saying that the inner class is
non-static but does not reference the enclosing class.

Change-Id: I31c9558a1c6ee530dccb45b16d165ed466904665
Signed-off-by: Edwin Kempin <ekempin@google.com>

gerrit-acceptance-tests/src/test/java/com/google/gerrit/acceptance/rest/change/DraftChangeIT.java

diff --git a/gerrit-acceptance-tests/src/test/java/com/google/gerrit/acceptance/rest/change/DraftChangeIT.java b/gerrit-acceptance-tests/src/test/java/com/google/gerrit/acceptance/rest/change/DraftChangeIT.java
index eefd64a..da7d7b5 100644
--- a/gerrit-acceptance-tests/src/test/java/com/google/gerrit/acceptance/rest/change/DraftChangeIT.java
+++ b/gerrit-acceptance-tests/src/test/java/com/google/gerrit/acceptance/rest/change/DraftChangeIT.java
@@ -277,7 +277,7 @@
     return revisionInfos.stream().map(revisionInfo -> revisionInfo.draft).collect(toList());
   }
 
-  private class MarkChangeAsDraftUpdateOp implements BatchUpdateOp {
+  private static class MarkChangeAsDraftUpdateOp implements BatchUpdateOp {
     @Override
     public boolean updateChange(ChangeContext ctx) throws Exception {
       Change change = ctx.getChange();