composer: Allow phpunit-bridge 6.0

This is required for PHP 8.4 support.

On master this was done in 66215a6.

Author: jtojnar

composer.json

@@ -32,7 +32,7 @@
     "require-dev": {
         "friendsofphp/php-cs-fixer": "^2.14",
         "monolog/monolog": "^1.24|^2.1",
-        "symfony/phpunit-bridge": "^4.4|^5.3"
+        "symfony/phpunit-bridge": "^4.4|^5.3|^6.0"
     },
     "suggest": {
         "ext-tidy": "Used to clean up given HTML and to avoid problems with bad HTML structure."