Fix invalid actions/checkout version (v6 → v4)

Co-authored-by: lindseywild <35239154+lindseywild@users.noreply.github.com>

Author: Copilot

.github/workflows/test-copilot-pr-creation.yml

@@ -25,7 +25,7 @@ jobs:
         site: ["sites/site-with-errors"]
     steps:
       - name: Checkout
-        uses: actions/checkout@v6
+        uses: actions/checkout@v4
 
       - name: Setup Ruby
         uses: ruby/setup-ruby@6ca151fd1bfcfd6fe0c4eb6837eb0584d0134a0c