minor #6107 Drop support of PHPUnit v7 dependency (keradus)

This PR was merged into the master branch.

Discussion
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Drop support of PHPUnit v7 dependency

ref https://github.com/FriendsOfPHP/PHP-CS-Fixer/pull/6067#issuecomment-963165765

Commits
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46b3f8521 Drop support of PHPUnit v7 dependency

composer.json

@@ -43,7 +43,7 @@
         "php-cs-fixer/phpunit-constraint-xmlmatchesxsd": "^1.2.1",
         "phpspec/prophecy": "^1.10.3",
         "phpspec/prophecy-phpunit": "^1.1 || ^2.0",
-        "phpunit/phpunit": "^7.5.20 || ^8.5.14 || ^9.5",
+        "phpunit/phpunit": "^8.5.21 || ^9.5",
         "phpunitgoodpractices/polyfill": "^1.5",
         "phpunitgoodpractices/traits": "^1.9.1",
         "symfony/phpunit-bridge": "^5.2.4",