ci: gate expensive test workflows at the job level (#40718)

Co-authored-by: Claude Code <noreply@anthropic.com>

.github/workflows/superset-python-unittest.yml

@@ -15,7 +15,27 @@ concurrency:
   cancel-in-progress: true
 
 jobs:
+  changes:
+    runs-on: ubuntu-24.04
+    permissions:
+      contents: read
+      pull-requests: read
+    outputs:
+      python: ${{ steps.check.outputs.python }}
+    steps:
+      - name: Checkout
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6
+        with:
+          persist-credentials: false
+      - name: Check for file changes
+        id: check
+        uses: ./.github/actions/change-detector/
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}
+
   unit-tests:
+    needs: changes
+    if: needs.changes.outputs.python == 'true'
     runs-on: ubuntu-24.04
     permissions:
       id-token: write
@@ -30,25 +50,17 @@ jobs:
         with:
           persist-credentials: false
           submodules: recursive
-      - name: Check for file changes
-        id: check
-        uses: ./.github/actions/change-detector/
-        with:
-          token: ${{ secrets.GITHUB_TOKEN }}
       - name: Setup Python
         uses: ./.github/actions/setup-backend/
-        if: steps.check.outputs.python
         with:
           python-version: ${{ matrix.python-version }}
       - name: Python unit tests
-        if: steps.check.outputs.python
         env:
           SUPERSET_TESTENV: true
           SUPERSET_SECRET_KEY: not-a-secret
         run: |
           pytest --durations-min=0.5 --cov-report= --cov=superset ./tests/common ./tests/unit_tests --cache-clear --maxfail=50
       - name: Python 100% coverage unit tests
-        if: steps.check.outputs.python
         env:
           SUPERSET_TESTENV: true
           SUPERSET_SECRET_KEY: not-a-secret