Bug report

Trying out PHPStan v2.0.1, I started noticing in various reports the type array<mixed, mixed>. I believe the largest possible array value is array<int|string, mixed>, so should it even be possible to instantiate a type larger than that?

I ran into the following error which, unless I'm missing something, makes no sense:

Parameter #1 $a of function foo expects array<int|string, mixed>, array<mixed> given.
  argument.type                                                                      

Type array<mixed> should always be equivalent to array<int|string, mixed>.

Code snippet that reproduces the problem

https://phpstan.org/r/b6e2e23b-0605-4956-bced-a5b8be0682de

Expected output

No error

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