chore: add checkout and prepare to contributors.yml

Author: JoshuaKGoldberg

.github/workflows/contributors.yml

@@ -2,6 +2,10 @@ jobs:
   contributors:
     runs-on: ubuntu-latest
     steps:
+      - uses: actions/checkout@v3
+        with:
+          fetch-depth: 0
+      - uses: ./.github/actions/prepare
       - uses: JoshuaKGoldberg/[email protected]
       - uses: stefanzweifel/git-auto-commit-action@v4
         with: