Update phpunit/phpunit requirement from ^8.5.37 to ^8.5.38 (#533)

Updates the requirements on [phpunit/phpunit](https://github.com/sebastianbergmann/phpunit) to permit the latest version.
- [Release notes](https://github.com/sebastianbergmann/phpunit/releases)
- [Changelog](https://github.com/sebastianbergmann/phpunit/blob/8.5.38/ChangeLog-8.5.md)
- [Commits](sebastianbergmann/phpunit@8.5.37...8.5.38)

---
updated-dependencies:
- dependency-name: phpunit/phpunit
  dependency-type: direct:development
...

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

Author: dependabot[bot]

composer.json

@@ -31,7 +31,7 @@
         "phpstan/extension-installer": "^1.3.1",
         "phpstan/phpstan": "^1.10.66",
         "phpstan/phpstan-phpunit": "^1.3.16",
-        "phpunit/phpunit": "^8.5.37"
+        "phpunit/phpunit": "^8.5.38"
     },
     "suggest": {
         "ext-mbstring": "for parsing UTF-8 CSS"