Revert "Support for PHP Code Coverage 8.0"

This reverts commit c9265a3.

Author: matthiasnoback

composer.json

@@ -5,7 +5,7 @@
   "require": {
     "php": "^7.1",
     "webmozart/assert": "^1.2",
-    "phpunit/php-code-coverage": "^4.0 || ^5.2 || ^6.0 || ^7.0 || ^8.0",
+    "phpunit/php-code-coverage": "^4.0 || ^5.2 || ^6.0 || ^7.0",
     "phpunit/phpunit": "^5.7 || ^6.0 || ^7.0 || ^8.0 || ^9.0"
   },
   "autoload": {