deployment-pr.yml: do not deploy the same PR at the same time

Else the second deployment fails if you push to fast
to the same PR.
The default behaviour is that the previous deployment is canceled.

.github/workflows/deployment-pr.yml

@@ -4,6 +4,10 @@ on:
   pull_request_target:
     types: [opened, reopened, labeled, synchronize]
 
+concurrency:
+  group: ${{ github.workflow}}-${{ github.event.pull_request.number }}
+  cancel-in-progress: true
+
 jobs:
   build-and-push:
     if: contains(github.event.pull_request.labels.*.name, 'deploy!')