Literal strings should be assignable to `Sequence[Unknown]`

Found this while analyzing common ecosystem false positives. I think this should work?
```py
from typing import Sequence, Any

seq: Sequence[Any] = "abc"  #  `Literal["abc"]` is not assignable to `Sequence[Any]`
```
https://play.ty.dev/1059069f-082c-4e2f-a643-92b3f0d8583c

Both of these cases work:
```py
seq: Sequence[Any] = some_str
seq: Sequence[str] = "abc"
```