Bug report

Hi, i think the following is a bug https://phpstan.org/r/3852d3d0-5965-4945-be76-012889331d21 as key 4 is not defined.
I would like to point out that if no (partial) match is found in the caller, PHPStan raise an error https://phpstan.org/r/44be467d-deef-4b69-8914-2273fca08b8f so the bug seems in checks and not in return type values assignment.

Moreover if that's not a bug I think it's at best a really confusing behaviour.

Code snippet that reproduces the problem

No response

Expected output

PHPStan to warn about index 4 not defined

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