Update phpunit/phpunit requirement from ^10.5.19 to ^10.5.20 (#105)

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/10.5.20/ChangeLog-10.5.md)
- [Commits](sebastianbergmann/phpunit@10.5.19...10.5.20)

---
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>

composer.json

@@ -17,7 +17,7 @@
   },
   "require-dev": {
     "doctrine/coding-standard": "^12.0",
-    "phpunit/phpunit": "^10.5.19",
+    "phpunit/phpunit": "^10.5.20",
     "psalm/plugin-phpunit": "^0.19.0",
     "vimeo/psalm": "^5.23"
   },