Property A::$map (Ds\Map<string, string>) does not accept Ds\Map<mixed, mixed>.

# Bug report

Same as https://github.com/phpstan/phpstan/issues/6757, it should be possible to initialize the map's types using property assigment


### Code snippet that reproduces the problem

https://phpstan.org/r/d3ca1078-268f-48da-a313-a874a5362da6
