Replace actions/checkout with plain git in deploy-qa job

Self-hosted qa runner has no node in PATH, so the Node-based
actions/checkout@v4 action can't run there. Swap it for a bash git
fetch/checkout, matching the pipeline's no-marketplace-action convention.

.github/workflows/ci.yml

@@ -42,7 +42,14 @@ jobs:
       JWT_SECRET_KEY: ${{ secrets.JWT_SECRET_KEY }}
       QA_ADMIN_PORT: ${{ vars.QA_ADMIN_PORT }}
     steps:
-      - uses: actions/checkout@v4
+      # actions/checkout@v4 is a Node-based action; this runner has no node
+      # in PATH, so checkout plain git instead of via marketplace action.
+      - name: Checkout
+        run: |
+          git init -q .
+          git remote add origin "${{ github.server_url }}/${{ github.repository }}.git"
+          git -c http.extraheader="AUTHORIZATION: bearer ${{ github.token }}" fetch --depth=1 origin "${{ github.sha }}"
+          git checkout -q FETCH_HEAD
 
       - name: Deploy to QA
         run: ./scripts/ci/deploy-qa.sh