Merge pull request #575 from beeware/firebase

Update ci.yml

.github/workflows/ci.yml

@@ -9,11 +9,9 @@ jobs:
     runs-on: ubuntu-latest
     if: contains(github.event.pull_request.labels.*.name, 'preview')
     steps:
-      - uses: actions/checkout@v1
-        with:
-          ref: "refs/pull/${{ github.event.number }}/merge" # THIS IS INSECURE
+      - uses: actions/checkout@v4
       - name: Set up Python
-        uses: actions/setup-python@v1
+        uses: actions/setup-python@v5
         with:
           python-version: '3.X'
       - name: Install dependencies