dogfood the new setup-dart action (#2017)

* dogfood the new setup-dart action

* update the labeler.yml file

* more tweaks to the labeling config

* revert pull_request_label.yml change

Author: devoncarew

.github/labeler.yml

@@ -13,7 +13,5 @@
   - webdev/**/*
 
 'dart-debug-extension':
-  - dwds/debug_extension_mv3
-
-'dart-debug-extension':
-  - dwds/debug_extension
+  - dwds/debug_extension/**/*
+  - dwds/debug_extension_mv3/**/*