Update phpunit/phpunit requirement from ^8.4.2 to ^8.4.3

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-8.4.md)
- [Commits](sebastianbergmann/phpunit@8.4.2...8.4.3)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

composer.json

@@ -19,7 +19,7 @@
         "phpstan/phpstan-deprecation-rules": "^0.10",
         "phpstan/phpstan-phpunit": "^0.10",
         "phpstan/phpstan-strict-rules": "^0.10",
-        "phpunit/phpunit": "^8.4.2"
+        "phpunit/phpunit": "^8.4.3"
     },
     "autoload": {
         "psr-4": {