Follow the practice of adding dependencies

tox.ini

@@ -37,10 +37,10 @@ skip_install = true
 deps =
     readme_renderer
     twine
+    -r{toxinidir}/requirements.txt
 commands =
     # https://github.com/pypa/twine/issues/977
     python -m pip install importlib_metadata==7.2.1 build
-    python -m pip install requirements.txt
     python -m build --no-isolation
     twine check dist/*