Fix python-tests workflow: split get_sample_dirs into its own job (#1420)

* Fix python-tests workflow: split get_sample_dirs into its own job

The build job declares `needs: get_sample_dirs`, but get_sample_dirs was
defined as a step inside build rather than as a separate job. This caused
GitHub Actions to reject the workflow with:

  The workflow must contain at least one job with no dependencies.

This commit:
- Extracts get_sample_dirs into its own job with proper outputs
- Replaces undefined $PYTHON_DIR with the actual path (samples/python)
- Formats the find output as JSON array for fromJson() compatibility
- Adds an if condition to skip the build matrix when no samples exist

Signed-off-by: Salman Muin Kayser Chishti <13schishti@gmail.com>

* Update actions/checkout from v4 to v6

---------

Signed-off-by: Salman Muin Kayser Chishti <13schishti@gmail.com>
Co-authored-by: Kristopher Overholt <koverholt@google.com>

Author: salmanmkc

.github/workflows/python-tests.yaml

@@ -33,29 +33,38 @@ on:
     - cron: "0 0 * * 0"
 
 jobs:
+  get_sample_dirs:
+    runs-on: ubuntu-latest
+    outputs:
+      sample_dirs: ${{ steps.get_dirs.outputs.sample_dirs }}
+    steps:
+      - uses: actions/checkout@v6
+        with:
+          ref: ${{ github.event.pull_request.head.sha }}
+
+      - name: Get Sample Directories
+        id: get_dirs
+        run: |
+          SAMPLE_DIRS=$( find samples/python -type d -not -path "*/.venv*" -exec test -e '{}'/requirements.txt \; -print | jq -R -s -c 'split("\n") | map(select(. != ""))' )
+          echo "sample_dirs=$SAMPLE_DIRS" >> $GITHUB_OUTPUT
+          echo "SAMPLE_DIRS: $SAMPLE_DIRS"  # For debugging
+
   build:
     runs-on: ubuntu-latest
+    needs:
+      - get_sample_dirs
+    if: ${{ needs.get_sample_dirs.outputs.sample_dirs != '[]' }}
     strategy:
       matrix:
         python-version: ["3.9", "3.10", "3.11", "3.12"]
         sample_dir: ${{ fromJson(needs.get_sample_dirs.outputs.sample_dirs) }}
       fail-fast: false # Important: Don't stop if one matrix configuration fails
 
-    needs:
-      - get_sample_dirs
-
     steps:
       - uses: actions/checkout@v6
         with:
           ref: ${{ github.event.pull_request.head.sha }}
 
-      - name: Get Sample Directories
-        id: get_sample_dirs
-        run: |
-          SAMPLE_DIRS=$( find $PYTHON_DIR -type d -not -path "*/.venv*" -exec test -e '{}'/requirements.txt \; -print )
-          echo "sample_dirs=$SAMPLE_DIRS" >> $GITHUB_OUTPUT
-          echo "SAMPLE_DIRS: $SAMPLE_DIRS"  # For debugging
-
       - name: Set up Python ${{ matrix.python-version }}
         uses: actions/setup-python@v6
         with:
@@ -91,4 +100,4 @@ jobs:
             pytest.txt
             ./htmlcov/
           retention-days: 30
-        if: ${{ always() }}
+        if: ${{ always() }}