CI-Workflow updates (#6481)

* Use `github.ref` for the `concurrency` group, hoping that previous WF
  run works with that (see comment in this PR below).
* The `Ci Success` step doesn't need to be a matrix job

.github/workflows/ci.yml

@@ -50,7 +50,7 @@ on:
 concurrency:
   # PRs: 1 CI run concurrently
   # main branch: 1 CI run per commit (so every commit is checked)
-  group: ${{ github.workflow }}-${{ github.event_name }}-${{ github.event.head_commit.id }}-${{ github.event.pull_request.head.ref }}
+  group: ${{ github.workflow }}-${{ github.event_name }}-${{ github.event.head_commit.id }}-${{ github.ref }}
   cancel-in-progress: true
 
 jobs:
@@ -817,10 +817,6 @@ jobs:
       # published.
       - helm-testing
       - site
-    strategy:
-      max-parallel: 2
-      matrix:
-        java-version: ['11'] # Ideally also '17', but GH concurrent job limit ... :(
     steps:
       # Intentionally empty job (for all GH WF) events so that the "required checks" setting
       # only needs to contain this job as the only required check for PRs.