Type of `tuple[()]` should evaluate to `Sequence[Never]` rather than `Sequence[Unknown]`

The typing spec has clarified that `tuple[()]` should evaluate to `Sequence[Never]`.

```python
T = TypeVar("T")

def test_seq(x: Sequence[T]) -> Sequence[T]:
    return x

def func8(t3: tuple[()]):
    assert_type(test_seq(t3), Sequence[Never])
```