IONOS(ci): Include PR number in concurrency group for pull requests

Update concurrency group definition to use github.event.number for pull
requests. This ensures each PR gets its own concurrency group, preventing
PRs from canceling each other's builds while still allowing new commits
to the same PR to cancel previous runs.

Signed-off-by: Misha M.-Kupriyanov <kupriyanov@strato.de>

Author: printminion-co

.github/workflows/build-artifact.yml

@@ -56,7 +56,7 @@ concurrency:
       github.event_name == 'pull_request' && format('pr-{0}', github.event.pull_request.number) ||
       (
         (
-          contains(fromJson('["refs/heads/ionos-dev"]'), github.ref) ||
+          contains(fromJson('["refs/heads/ionos-dev","refs/heads/ionos-stable"]'), github.ref) ||
           startsWith(github.ref, 'refs/heads/rc/')
         ) && github.run_id ||
         github.ref