Error on assignment of new generic subclass instance

# Bug report

### Discussed in https://github.com/phpstan/phpstan/discussions/8218

<div type='discussions-op-text'>

<sup>Originally posted by **butesa** October 26, 2022</sup>
Hello,

https://phpstan.org/r/39ec7180-b0c9-4691-b83d-19e3bbf999e3

why is there an error on line 53 (new B), but no error on line 52 (new A)?

Thank you very much.</div>