[ty] Fix call argument validation for variadic parameters (#30086)
Fixes a small bug in argument validation involving variadic parameter
types where we sometimes use the type inferred without type context
rather than the type inferred against the parameter:
```py
@overload
def pair[T: int, U](*args: *tuple[list[T], list[U]]) -> tuple[T, U]: ...
@overload
def pair(first: list[str], second: list[int], /) -> tuple[str, int]: ...
def pair(*args: object) -> object:
raise NotImplementedError
reveal_type(pair([42], ["x"])) # main: tuple[Unknown, Unknown], now: tuple[int, str]
```
