Build(deps-dev): Update phpunit/phpunit requirement

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/master/ChangeLog-9.1.md)
- [Commits](sebastianbergmann/phpunit@9.1.3...9.1.4)

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

Author: dependabot-preview[bot]

composer.json

@@ -23,7 +23,7 @@
     },
     "require-dev": {
         "ext-json": "*",
-        "phpunit/phpunit": "^9.1.3"
+        "phpunit/phpunit": "^9.1.4"
     },
     "config": {
         "preferred-install": "dist",