False positive for "Unnecessary isinstance call"

From version 1.1.380 onwards, Pyright erroneously reports the `isinstance` below as unnecessary:

```python
class A:
    ...
    
class B(A):
    ...

class C(A):
    ...

def f(elem: B | C, _type: type[A]) -> bool:
    return isinstance(elem, _type)

assert f(B(), B)
assert not f(B(), C)
```

That would be correct only if `type` were invariant.