Add check for COLLABORATOR (#3283)

Author: laurakwhit

.github/workflows/design-feedback-notify.yml

@@ -12,7 +12,7 @@ jobs:
   notify:
     if: >-
       github.event.label.name == 'DESIGN FEEDBACK REQUESTED' &&
-      github.event.pull_request.author_association == 'MEMBER'
+      contains(fromJSON('["MEMBER","COLLABORATOR"]'), github.event.pull_request.author_association)
     runs-on: ubuntu-latest
     steps:
       - name: Notify Slack