Added checks directory to mypy

Author: radarhere

tox.ini

@@ -30,4 +30,4 @@ skip_install = true
 deps =
     -r .ci/requirements-mypy.txt
 commands =
-    mypy conftest.py selftest.py setup.py docs src winbuild Tests {posargs}
+    mypy conftest.py selftest.py setup.py checks docs src winbuild Tests {posargs}