Build wheels using build.

Solves the issue with twine complaining about syntax errors in the
long_description.

templates/python.yml

@@ -17,11 +17,12 @@ build-wheel:
   extends: .python3-build
   script:
     - python3 setup.py check --verbose --metadata --restructuredtext --strict
-    - python3 setup.py bdist_wheel
+    - python3 -m build
   after_script:
-    - twine check dist/*.whl
+    - &twine_check twine check dist/*.whl
   artifacts:
     paths:
+      - dist/*.tar.gz
       - dist/*.whl
 
 .install-wheel:
@@ -48,7 +49,7 @@ pypi-upload:
   extends: .python3-build
   stage: deploy
   script:
-    - twine check dist/*
+    - *twine_check
     - twine upload --config-file "$pypirc" dist/*
   rules:
     - if: $CI_COMMIT_TAG && ($SKIP_PYPI_UPLOAD == null)