IONOS(ci): Use head_ref fallback in concurrency group

Update concurrency group to use github.head_ref with ref_name fallback
instead of ref. This provides better isolation for pull request builds
while maintaining compatibility with branch builds.

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

Author: printminion-co

.github/workflows/build-artifact.yml

@@ -52,8 +52,8 @@ on:
 concurrency:
   group: >-
     ${{ github.workflow }}-${{
-      github.ref == 'refs/heads/ionos-dev' && github.run_id ||
       github.event.pull_request.number ||
+      github.ref == 'refs/heads/ionos-dev' && github.run_id ||
       github.ref
     }}
   cancel-in-progress: true