[CI] Fix: Run auto-assign check if user is a prev contributor (#5873)

Author: gregfromstl

.github/workflows/auto-assign.yml

@@ -13,6 +13,7 @@ jobs:
     if: |
       github.event.pull_request.author_association == 'MEMBER' ||
       github.event.pull_request.author_association == 'OWNER' ||
-      github.event.pull_request.author_association == 'COLLABORATOR'
+      github.event.pull_request.author_association == 'COLLABORATOR' ||
+      github.event.pull_request.author_association == 'CONTRIBUTOR'
     steps:
       - uses: toshimaru/auto-author-assign@v2.1.1