Update labeler.yml (#4234)

## What are you changing in this pull request and why?

Attempting to fix the labeler workflow to only run once per PR.
Hopefully this will stop causing it to remove the First time contributor
label!

.github/workflows/labeler.yml

@@ -5,8 +5,8 @@
 
 name: "Pull Request Labeler"
 on:
-- pull_request_target
-
+  pull_request_target:
+    types: [opened]
 jobs:
   triage:
     permissions: