Fatal error: During class fetch: Uncaught PHPStan\Broker\ClassAutoloadingException: Class Atk4\Ui\SessionTrait not found.

# Bug report

autoload error can be caught, phpstan should report that instead of a fatal error

### Code snippet that reproduces the problem

https://github.com/atk4/login/runs/5111504969?check_suite_focus=true#step:10:6

### Expected output

non-ignoreable error that such class failed to load