strval accepts Stringable objects as an argument, but PHPStan reports an error.

https://phpstan.org/r/513ed638-5c42-4114-9e92-e61fd6b78ee4

This issue can be reproduced on the current HEAD of 1.10.x branch, but not on the latest release 1.10.14.
It seems to be introduced by phpstan/phpstan-src#2354.

This breaks the integration test of phpstan-src repository.
https://github.com/phpstan/phpstan-src/actions/runs/4899797660/jobs/8750045570