fix: Add setuptools as an explicit test dependency

Author: nifflets

tox.ini

@@ -21,6 +21,7 @@ deps =
     twine
     isort
     mypy
+    setuptools
 commands =
     black --check src tests setup.py conftest.py --exclude tests/test_functions/background_load_error/main.py
     isort -c src tests setup.py conftest.py