Switch checkout in prepare-release.yml to v3 (#2126)

Author: Quinn-With-Two-Ns

.github/workflows/prepare-release.yml

@@ -145,7 +145,8 @@ jobs:
       ACTIONS_ALLOW_USE_UNSECURE_NODE_VERSION: true
     steps:
       - name: Checkout repo
-        uses: actions/checkout@v4
+        # FIXME: v4+ requires Node 20
+        uses: actions/checkout@v3
         with:
           ref: ${{ env.INPUT_REF }}