check ninja not present

Author: mayeut

.github/workflows/build.yml

@@ -128,6 +128,9 @@ jobs:
           name: cibw-sdist
           path: sdist
 
+      - name: Ensure Ninja not present on the system
+        run: if which ninja; false; fi
+
       - name: Install SDist
         run: pip install --no-binary=ninja $(ls sdist/*.tar.gz)[test] -Ccmake.define.BUILD_CMAKE_FROM_SOURCE=OFF