CommitValidation: Keep relaying warning messages from validators

In 5eb0219 - Set logging tag with plugin name on invocation of ...
Running onCommitRecieved for all CommitValidationListeners was
refactored from a for-loop to PluginSetContex#runEach.
Adding messages from the successful validations was lost in the
process.

Bug: Issue 10666
Change-Id: If81489b38b107a5f04c33b398fb554ac2516776f
diff --git a/java/com/google/gerrit/server/git/validators/CommitValidators.java b/java/com/google/gerrit/server/git/validators/CommitValidators.java
index b228267..c6d26b5 100644
--- a/java/com/google/gerrit/server/git/validators/CommitValidators.java
+++ b/java/com/google/gerrit/server/git/validators/CommitValidators.java
@@ -487,7 +487,8 @@
       List<CommitValidationMessage> messages = new ArrayList<>();
       try {
         commitValidationListeners.runEach(
-            l -> l.onCommitReceived(receiveEvent), CommitValidationException.class);
+            l -> messages.addAll(l.onCommitReceived(receiveEvent)),
+            CommitValidationException.class);
       } catch (CommitValidationException e) {
         messages.addAll(e.getMessages());
         throw new CommitValidationException(e.getMessage(), messages);