typing: Correct type of TestCase.skipTest

This raises an exception so we will never return. Correcting
this allows type checkers to use the check for type narrowing.

Signed-off-by: Stephen Finucane <stephen@that.guru>

Author: stephenfin

testtools/testcase.py

@@ -23,7 +23,7 @@
 import types
 import unittest
 from collections.abc import Callable, Iterator
-from typing import TYPE_CHECKING, ParamSpec, TypeVar, cast, overload
+from typing import TYPE_CHECKING, NoReturn, ParamSpec, TypeVar, cast, overload
 from unittest.case import SkipTest
 
 T = TypeVar("T")
@@ -366,7 +366,7 @@ def patch(self, obj: object, attribute: str, value: object) -> None:
     def shortDescription(self) -> str:
         return self.id()
 
-    def skipTest(self, reason: str) -> None:  # type: ignore[override]
+    def skipTest(self, reason: str) -> NoReturn:
         """Cause this test to be skipped.
 
         This raises self.skipException(reason). skipException is raised