move rollout to separate job

.forgejo/workflows/build-synapse.yaml

@@ -19,8 +19,15 @@ jobs:
           tags: git.janky.solutions/jankysolutions/infra/synapse:latest
           platforms: linux/amd64
           push: ${{ github.ref == 'refs/heads/main' }}
+  rollout:
+    name: roll out update
+    runs-on: ubuntu-latest
+    container:
+      image: git.janky.solutions/jankysolutions/infra/deployer:latest
+    needs: [build-synapse]
+    if: github.ref == 'refs/heads/main'
+    steps:
       - name: roll out update
-        if: github.ref == 'refs/heads/main'
         run: |
           set -euo pipefail
           echo "${{ secrets.KUBERNETES_CLIENT_CONFIG }}" > ~/.kube/config