Use new github output mechanism to set the date.

.github/workflows/rollout-dashboard.yaml

@@ -23,7 +23,7 @@ jobs:
     steps:
       - name: Set month and year for cache key
         id: date
-        run: echo "::set-output name=date::$(date +'%Y-%m')"
+        run: echo "date=$(date +'%Y-%m')" >> "$GITHUB_OUTPUT"
       - uses: actions/checkout@v4
       - name: Move backend files to source root
         run: mv -f rollout-dashboard/server/* .