allow `ParamSpec.args` on its own

```py
def f1(a: int, *, b: str=""): ...
def f2(a: int, *, b: str): ...
def call[**P](fn: Callable[P, None], *args: P.args):
fn(*args)
call(f1, 1) # ok
call(f2, 1) # error
```

The issue names no implementation files, tests, or entry points. Start by reproducing the shown ParamSpec.args calls and locate the type-checking path for standalone ParamSpec.args; done means the f1 call remains accepted while the f2 call is rejected.

Written by the indexing model from the issue text.