Degrade PHPUnit to version 8

Author: jasonmccreary

composer.json

@@ -16,7 +16,7 @@
         "doctrine/dbal": "^2.9"
     },
     "require-dev": {
-        "phpunit/phpunit": "^8.0|^9.0",
+        "phpunit/phpunit": "^8.0",
         "mockery/mockery": "^1.3",
         "orchestra/testbench": "^4.0|^5.0"
     },