Only log missed ChangeListener events in debug mode

There's no point in spamming an install's error_log just
because hooks-its hasn't handled a specific event type.

Change-Id: I3e67a6e83f0944ae1d53395cd2405f38be775050
diff --git a/hooks-its/src/main/java/com/googlesource/gerrit/plugins/hooks/workflow/GerritHookFilter.java b/hooks-its/src/main/java/com/googlesource/gerrit/plugins/hooks/workflow/GerritHookFilter.java
index 10b13d6..b89d1b3 100644
--- a/hooks-its/src/main/java/com/googlesource/gerrit/plugins/hooks/workflow/GerritHookFilter.java
+++ b/hooks-its/src/main/java/com/googlesource/gerrit/plugins/hooks/workflow/GerritHookFilter.java
@@ -172,7 +172,7 @@
       } else if (event instanceof RefUpdatedEvent) {
         doFilter((RefUpdatedEvent) event);
       } else {
-        log.info("Event " + event + " not recognised and ignored");
+        log.debug("Event " + event + " not recognised and ignored");
       }
     } catch (Throwable e) {
       log.error("Event " + event + " processing failed", e);