False positive when using match expression to narrow types

[axlon]

Bug report

It appears that PHPStan doesn't narrow types that are part of a match expression's condition, which leads to false positives when a match expression is used to eliminate certain types from a union.

Code snippet that reproduces the problem

https://phpstan.org/r/1b12aa5c-1398-4065-a014-80cfe3c45916

Expected output

No errors. We already know that the object cannot be null because we ended up in the false match arm.

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