Bump phpstan/phpstan-phpunit from 1.3.16 to 1.4.0

Bumps [phpstan/phpstan-phpunit](https://github.com/phpstan/phpstan-phpunit) from 1.3.16 to 1.4.0.
- [Release notes](https://github.com/phpstan/phpstan-phpunit/releases)
- [Commits](phpstan/phpstan-phpunit@1.3.16...1.4.0)

---
updated-dependencies:
- dependency-name: phpstan/phpstan-phpunit
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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