Fix typo in  BazelUtils.showFailedActions(events)

Change-Id: I576e292fa32ca200a20142a2ca077652108f175c

jenkins/lib/src/build/bazel/ci/BazelUtils.groovy

diff --git a/jenkins/lib/src/build/bazel/ci/BazelUtils.groovy b/jenkins/lib/src/build/bazel/ci/BazelUtils.groovy
index 2614187..43029fd 100644
--- a/jenkins/lib/src/build/bazel/ci/BazelUtils.groovy
+++ b/jenkins/lib/src/build/bazel/ci/BazelUtils.groovy
@@ -113,13 +113,13 @@
     def eventsstring = ""
     for(event in events) {
       if ("action" in event) {
-        eventstring = eventstring + event + "\n"
+        eventsstring += event + "\n"
       }
     }
     if (eventsstring == "") {
       script.echo("No failed actions reported in the event stream")
     } else {
-      script.echo("Failed actions:\n" + eventstring)
+      script.echo("Failed actions:\n" + eventsstring)
     }
   }