Bump phpstan/phpstan-strict-rules from 1.5.5 to 1.6.0

Bumps [phpstan/phpstan-strict-rules](https://github.com/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-strict-rules
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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