add sphinx tests; compare to .azure-pipelines/templates/steps/sphinx-steps.yml which is still needed for other pipelines on azure

.github/workflows/sphinx_steps.yml

@@ -0,0 +1,37 @@
+name: Sphinx steps
+on:
+  workflow_call:
+permissions:
+  contents: read
+
+jobs:
+  test_sphinx_builds:
+    name: Build Sphinx Documentation
+    runs-on: ubuntu-latest
+    steps:
+      - name: checkout
+        uses: actions/checkout@v6.0.2
+      - name: Build Sphinx Documentation
+        run: |-
+          set -e
+          sudo apt-get update
+          sudo apt-get install -y --no-install-recommends libaugeas-dev
+          FINAL_STATUS=0
+          declare -a FAILED_BUILDS
+          tools/venv.py
+          source venv/bin/activate
+          for doc_path in */docs
+          do
+            echo ""
+            echo "##[group]Building $doc_path"
+            if ! sphinx-build -W --keep-going -b html $doc_path $doc_path/_build/html; then
+              FINAL_STATUS=1
+              FAILED_BUILDS[${#FAILED_BUILDS[@]}]="${doc_path%/docs}"
+            fi
+            echo "##[endgroup]"
+          done
+          if [[ $FINAL_STATUS -ne 0 ]]; then
+            echo "##[error]The following builds failed: ${FAILED_BUILDS[*]}"
+            exit 1
+          fi
+        shell: bash