Expand `NamedExpr` range to include full range of parenthesized value (#6632)
## Summary
Given:
```python
if (
x
:=
( # 4
y # 5
) # 6
):
pass
```
It turns out the parser ended the range of the `NamedExpr` at the end of
`y`, rather than the end of the parenthesis that encloses `y`. This just
seems like a bug -- the range should be from the start of the name on
the left, to the end of the parenthesized node on the right.
## Test Plan
`cargo test`