Python template: Run setuptools check only if setup.py exists.

templates/python.yml

@@ -16,7 +16,9 @@
 build-wheel:
   extends: .python3-build
   script:
-    - python3 setup.py check --verbose --metadata --restructuredtext --strict
+    - >-
+      [ ! -f setup.py ] ||
+      python3 setup.py check --verbose --metadata --restructuredtext --strict
     - python3 -m build
   after_script:
     - &twine_check twine check dist/*.whl