build(deps-dev): bump phpunit/phpunit from 8.5.23 to 9.5.16 (#141)

Bumps [phpunit/phpunit](https://github.com/sebastianbergmann/phpunit) from 8.5.23 to 9.5.16.
- [Release notes](https://github.com/sebastianbergmann/phpunit/releases)
- [Changelog](https://github.com/sebastianbergmann/phpunit/blob/master/ChangeLog-8.5.md)
- [Commits](sebastianbergmann/phpunit@8.5.23...9.5.16)

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

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

composer.json

@@ -27,7 +27,7 @@
         "php-http/mock-client": "^1.1",
         "phpspec/prophecy": "~1.15",
         "phpstan/phpstan": "^1.4",
-        "phpunit/phpunit": "^8"
+        "phpunit/phpunit": "^9"
     },
     "config": {
         "platform": {