Updated mypy pin (#490)

Regression in mypy v1.12 was resolved in v1.14. Use that as a minimum
pin (rather than clearing it) to force/suggest/trigger an update for
existing environments.

setup.cfg

@@ -39,9 +39,7 @@ zip_safe = false
 tests =
     pytest
     pytest-asyncio
-    # Pending release of https://github.com/python/mypy/pull/17355
-    # Likely in v1.13.1+, when pip can be removed.
-    mypy~=1.11.0
+    mypy>=1.14.0
 
 [tool:pytest]
 testpaths = tests