This release of php-actions/phpstan has tackled speed issues associated with previous versions, while maintaining (and enhancing) the configuration possibilities - you can still choose between PHP version and PHPStan version, but now you can also choose which PHP extensions are installed for your test runs, making the test runner extremely minimal with only the baseline required components.
Please note, to achieve the build speeds and configuration possibilities, the custom Docker image is pushed to the repository that calls the action. This means that your user or organisation will list the package on the page at https://github.com/{organisation}/packages. This shouldn't have any effect on things, but it's worth knowing about.