Use version_file instead of write_to in pyproject.toml

See #13 and https://setuptools-scm.readthedocs.io/en/latest/config/

{{cookiecutter.project_slug}}/.gitlab-ci.yml

@@ -88,7 +88,7 @@ run_unit_tests:
     - tox -e py3${PY_VERSION}
   parallel:
     matrix: # use the matrix for testing
-      - PY_VERSION: [7, 8, 9, 10]
+      - PY_VERSION: [ 8, 9, 10]
 
 # Run code coverage on the base image thus also performing unit tests
 run_unit_tests_coverage: