Bump phpstan/phpstan-phpunit from 0.12.17 to 0.12.18 (#153)

Bumps [phpstan/phpstan-phpunit](https://github.com/phpstan/phpstan-phpunit) from 0.12.17 to 0.12.18.
- [Release notes](https://github.com/phpstan/phpstan-phpunit/releases)
- [Commits](phpstan/phpstan-phpunit@0.12.17...0.12.18)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>