Add non-strict typechecking to test module

'strict' is a global flag, so I've had to break out the type-
checking options to be more specific

setup.cfg

@@ -16,5 +16,25 @@ exclude =
 junit_family=xunit2
 
 [mypy]
-files=cibuildwheel/
-strict=True
+python_version = 3.6
+files = cibuildwheel,test
+
+warn_unused_configs = True
+warn_redundant_casts = True
+
+[mypy-cibuildwheel]
+disallow_any_generics = True
+disallow_subclassing_any = True
+disallow_untyped_calls = True
+disallow_untyped_defs = True
+disallow_incomplete_defs = True
+check_untyped_defs = True
+disallow_untyped_decorators = True
+no_implicit_optional = True
+warn_unused_ignores = True
+warn_return_any = True
+no_implicit_reexport = True
+strict_equality = True
+
+[mypy-pytest,setuptools]
+ignore_missing_imports = True