Bump the dev-dependencies group with 2 updates

Bumps the dev-dependencies group with 2 updates: [phpstan/phpstan-phpunit](https://github.com/phpstan/phpstan-phpunit) and [phpstan/phpstan-strict-rules](https://github.com/phpstan/phpstan-strict-rules).


Updates `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)

Updates `phpstan/phpstan-strict-rules` from 1.5.5 to 1.6.0
- [Release notes](https://github.com/phpstan/phpstan-strict-rules/releases)
- [Commits](phpstan/phpstan-strict-rules@1.5.5...1.6.0)

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

Signed-off-by: dependabot[bot] <support@github.com>