Remove label trigger for triage workflow (#12124)

Every time I add labels to issues I routinely get emails about cancelled
workflows. I'm kind of tired of getting these emails so let's try
moving to just a cron for this workflow.

Author: alexcrichton

.github/workflows/triage.yml

@@ -1,8 +1,6 @@
 name: "Issue / PR Triage"
 
 on:
-  issues:
-    types: ["labeled"]
   schedule:
     # Run pull request triage once an hour. Ideally, this would be on
     # "labeled" types of pull request events, but that doesn't work if the pull