Make FixtureFuction type alias instead of TypeVar

[MarcoGorelli]

FixtureFunction only appears twice:

pytest/src/_pytest/fixtures.py

Line 1241 in 0e2846f

def __call__(self, function: FixtureFunction) -> FixtureFunctionDefinition:

pytest/src/_pytest/fixtures.py

Lines 1344 to 1352 in 0e2846f

	def fixture(
	fixture_function: FixtureFunction | None = None,
	*,
	scope: _ScopeName | Callable[[str, Config], _ScopeName] = "function",
	params: Iterable[object] | None = None,
	autouse: bool = False,
	ids: Sequence[object | None] | Callable[[Any], object | None] | None = None,
	name: str | None = None,
	) -> FixtureFunctionMarker | FixtureFunctionDefinition:

Both times, it only appears once in a function signature. Therefore, the TypeVar has no effect

pyright would warn about this too:

  /home/marcogorelli/pytest-dev/src/_pytest/fixtures.py:1241:34 - warning: TypeVar "FixtureFunction" appears only once in generic function signature
    Use "(...) -> object" instead (reportInvalidTypeVarUse)
  /home/marcogorelli/pytest-dev/src/_pytest/fixtures.py:1345:23 - warning: TypeVar "FixtureFunction" appears only once in generic function signature
    Use "(...) -> object" instead (reportInvalidTypeVarUse)

[bluetech]

Thanks!

[bluetech]

Since this is not a user-visible change we can skip the changelog, I added skip-news label.