Surprising type analysis failure

```python
class Node:
pass

class Wrapper:
def __init__(self, child: Node):
self.child = child

class SpecialNode(Node):
pass

def f(plan: Wrapper | None):
if not (plan and isinstance(plan.child, SpecialNode)):
return
ts1: SpecialNode = plan.child # Ok
ts2: SpecialNode = plan.child if plan else None # "None" is not assignable to declared type "SpecialNode"
```

Since `plan.child` is accessed successfully, I assume pyright knows that plan isn't None and that the extra condition `if plan` is a no-op. Hopefully this knowledge can be incorporated into the analysis.

Start by running the provided Python snippet through pyright and confirm the diagnostic on the conditional expression. Trace the type analysis for the `plan` guard and conditional expression; done means the `ts2` assignment is accepted when the earlier access establishes that `plan` is not None.

Written by the indexing model from the issue text.