ci(concurrency): make cancel-in-progress event-aware, group by sha on push

Yesterday two PRs (#9724 llama.cpp bump, #9731 llama-cpp-darwin
consolidation) merged 11 seconds apart. Both shared the same
backend.yml concurrency group (ci-backends-refs/heads/master-...) due
to "${{ github.head_ref || github.ref }}" — empty head_ref on push
events falls through to the static refs/heads/master. With
cancel-in-progress: true that meant the second merge cancelled the
first's in-flight backend builds. The first PR's CI never finished;
the second PR only touched CI files so its run was a no-op.

Two changes per workflow:
- group: replace "${{ github.head_ref || github.ref }}" with
  "${{ github.event.pull_request.number || github.sha }}". On PRs
  this groups by PR number (same as before, just keyed on number not
  branch name); on push events it groups per-commit, so two master
  pushes never share a group.
- cancel-in-progress: gate on github.event_name == 'pull_request' so
  rapid pushes to a PR still cancel old runs (newer push wins) but
  master pushes never cancel each other.

Trade-off vs alternatives:
- Merge queue would also solve this and additionally test the merged
  commit before it lands. Heavier process change; out of scope here.
- Allowing per-commit master concurrency means two simultaneous master
  runs may overlap and race on tag pushes, but each commit's manifest
  digest is unique and the registry is last-writer-wins on tags —
  newer commit's tag overwrites older.

Applied to 11 workflows that share the same concurrency pattern:
backend.yml, backend_pr.yml, image.yml, image-pr.yml, lint.yml,
test.yml, test-extra.yml, tests-e2e.yml, tests-aio.yml,
tests-ui-e2e.yml, generate_intel_image.yaml.

Assisted-by: Claude:claude-opus-4-7
Signed-off-by: Ettore Di Giacinto <mudler@localai.io>

.github/workflows/backend.yml

@@ -24,8 +24,8 @@ on:
   workflow_dispatch:
 
 concurrency:
-  group: ci-backends-${{ github.head_ref || github.ref }}-${{ github.repository }}
-  cancel-in-progress: true
+  group: ci-backends-${{ github.event.pull_request.number || github.sha }}-${{ github.repository }}
+  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
 
 jobs:
   generate-matrix:

.github/workflows/backend_pr.yml

@@ -4,8 +4,8 @@ on:
   pull_request:
 
 concurrency:
-  group: ci-backends-pr-${{ github.head_ref || github.ref }}-${{ github.repository }}
-  cancel-in-progress: true
+  group: ci-backends-pr-${{ github.event.pull_request.number || github.sha }}-${{ github.repository }}
+  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
 
 jobs:
   generate-matrix:

.github/workflows/generate_intel_image.yaml

@@ -7,8 +7,8 @@ on:
       - master
 
 concurrency:
-  group: intel-cache-${{ github.head_ref || github.ref }}-${{ github.repository }}
-  cancel-in-progress: true
+  group: intel-cache-${{ github.event.pull_request.number || github.sha }}-${{ github.repository }}
+  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
 
 jobs:
   generate_caches:

.github/workflows/image-pr.yml

@@ -5,8 +5,8 @@
     pull_request:
   
   concurrency:
-    group: ci-${{ github.head_ref || github.ref }}-${{ github.repository }}
-    cancel-in-progress: true
+    group: ci-${{ github.event.pull_request.number || github.sha }}-${{ github.repository }}
+    cancel-in-progress: ${{ github.event_name == 'pull_request' }}
   
   jobs:
     image-build:

.github/workflows/image.yml

@@ -9,8 +9,8 @@
         - '*'
   
   concurrency:
-    group: ci-${{ github.head_ref || github.ref }}-${{ github.repository }}
-    cancel-in-progress: true
+    group: ci-${{ github.event.pull_request.number || github.sha }}-${{ github.repository }}
+    cancel-in-progress: ${{ github.event_name == 'pull_request' }}
   
   jobs:
     hipblas-jobs:

.github/workflows/lint.yml

@@ -13,8 +13,8 @@ on:
       - master
 
 concurrency:
-  group: ci-lint-${{ github.head_ref || github.ref }}-${{ github.repository }}
-  cancel-in-progress: true
+  group: ci-lint-${{ github.event.pull_request.number || github.sha }}-${{ github.repository }}
+  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
 
 jobs:
   golangci-lint:

.github/workflows/test-extra.yml

@@ -10,8 +10,8 @@ on:
       - '*'
 
 concurrency:
-  group: ci-tests-extra-${{ github.head_ref || github.ref }}-${{ github.repository }}
-  cancel-in-progress: true
+  group: ci-tests-extra-${{ github.event.pull_request.number || github.sha }}-${{ github.repository }}
+  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
 
 jobs:
   detect-changes:

.github/workflows/test.yml

@@ -16,8 +16,8 @@ on:
       - '*'
 
 concurrency:
-  group: ci-tests-${{ github.head_ref || github.ref }}-${{ github.repository }}
-  cancel-in-progress: true
+  group: ci-tests-${{ github.event.pull_request.number || github.sha }}-${{ github.repository }}
+  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
 
 jobs:
   tests-linux:

.github/workflows/tests-aio.yml

@@ -22,8 +22,8 @@ on:
       - '*'
 
 concurrency:
-  group: ci-tests-aio-${{ github.head_ref || github.ref }}-${{ github.repository }}
-  cancel-in-progress: true
+  group: ci-tests-aio-${{ github.event.pull_request.number || github.sha }}-${{ github.repository }}
+  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
 
 jobs:
   tests-aio:

.github/workflows/tests-e2e.yml

@@ -16,8 +16,8 @@ on:
       - '*'
 
 concurrency:
-  group: ci-tests-e2e-backend-${{ github.head_ref || github.ref }}-${{ github.repository }}
-  cancel-in-progress: true
+  group: ci-tests-e2e-backend-${{ github.event.pull_request.number || github.sha }}-${{ github.repository }}
+  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
 
 jobs:
   tests-e2e-backend:

.github/workflows/tests-ui-e2e.yml

@@ -12,8 +12,8 @@ on:
       - master
 
 concurrency:
-  group: ci-tests-ui-e2e-${{ github.head_ref || github.ref }}-${{ github.repository }}
-  cancel-in-progress: true
+  group: ci-tests-ui-e2e-${{ github.event.pull_request.number || github.sha }}-${{ github.repository }}
+  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
 
 jobs:
   tests-ui-e2e: