Enable pylint's python 3.8 typing checks (unnecessary-default-type-args)

Author: Pierre-Sassoulas

src/_pytest/fixtures.py

@@ -91,7 +91,7 @@
 FixtureFunction = TypeVar("FixtureFunction", bound=Callable[..., object])
 # The type of a fixture function (type alias generic in fixture value).
 _FixtureFunc = Union[
-    Callable[..., FixtureValue], Callable[..., Generator[FixtureValue, None, None]]
+    Callable[..., FixtureValue], Callable[..., Generator[FixtureValue]]
 ]
 # The type of FixtureDef.cached_result (type alias generic in fixture value).
 _FixtureCachedResult = Union[
@@ -883,9 +883,7 @@ def call_fixture_func(
     fixturefunc: _FixtureFunc[FixtureValue], request: FixtureRequest, kwargs
 ) -> FixtureValue:
     if is_generator(fixturefunc):
-        fixturefunc = cast(
-            Callable[..., Generator[FixtureValue, None, None]], fixturefunc
-        )
+        fixturefunc = cast(Callable[..., Generator[FixtureValue]], fixturefunc)
         generator = fixturefunc(**kwargs)
         try:
             fixture_result = next(generator)