Give events ping a proper alias (#1300)

sql/org_mozilla_firefox_derived/event_types_v1/query.sql

@@ -5,9 +5,9 @@ WITH current_events AS (
       TIMESTAMP_ADD(submission_timestamp, INTERVAL timestamp MILLISECOND) AS timestamp
     )
   FROM
-    org_mozilla_firefox.events
+    org_mozilla_firefox.events e
   CROSS JOIN
-    UNNEST(events) AS event
+    UNNEST(e.events) AS event
   WHERE
     DATE(submission_timestamp) = @submission_date
 ),