Narrowing inside `try` is preserved into `finally`, ignoring type outside of `try`

### Describe the Bug

```python
from typing import *

def something_that_might_throw() -> None:
raise Exception()

class Thing():
def something(self) -> None:
pass

def blah() -> None:
x = None
try:
something_that_might_throw()
if x is None:
x = Thing()
except Exception:
raise
finally:
reveal_type(x) # revealed type: Thing, but it could be `None`
x.something()
```

Python: 3.12

### Sandbox Link

https://pyrefly.org/sandbox/?project=N4IgZglgNgpgziAXKOBDAdgEwEYHsAeAdAA4CeS4ATrgLYAEALqcROgOZ0Q3G6UN0AqADroRIzDDB04tGAwAWrNgH0FqBspoQ28jQuoB3ABQBKOgFoAfHQByudDEQi6LupVQQ4MOgFF8AYxhiBgh7U2dXSJF-KFQ4ODoAFUV2Uyd0SIkpGRo5FLYjLygwMytbe0cIyJdiOLgxLEk6bFj5UwtrOwd0yPw6AF5yhyrGSlIe6pccvKVVeXVNbV05w3CMyc4pPs8hyvWN1z7B5KU1yJgAoP4-QODQ9AnJ908YEch0VCgocZHIyhgAG4wT6qZgwIz4MwAYjcgOBsEwjDBiCS%2BQANM0AK78CD8fy4TFQRHYbwAAy6MFJv0OhGmClOJhAaJAZH%2BYG%2BhAYtCgFBhAAVSGzvtIMDgCHR8ehIGxMe4QvZCCIYQBlGDeXQMYhwRAAeh1rMkHN4bB1MHQOswuH8cB1kulsvU9x1dDAvDoqABHliLW8du0DvlGVwd3scEV6DICns5iBlDg9wGdCEIAAzIQAIwAJmTIgA2jBKNQ4wBdESY9BcHh8GCYcyYCD-fwhIGJgDk2nQvBgrZEnYY5n%2BAEdMQ2a%2BYANYwUjmVD%2BQLxNsGVCUdA99AgAC%2BzNnzZgADFoDAKGgsHgiGRN0A

### (Only applicable for extension issues) IDE Information

I'm not sure what the desired behavior is, but clearly we're guessing wrong in this case by taking the refined type from the `try`.

If we take the original type before the `try` then it doesn't account for the fact that the `try` could have succeeded. I thought we created a flow branch at the beginning of the try-block and merging the two branches should have handled this, but something is going wrong.