drop support for phpunit 8.0

Author: thekonz

composer.json

@@ -25,7 +25,7 @@
     },
     "require-dev": {
         "orchestra/testbench": "^7.0",
-        "phpunit/phpunit": "^8.0|^9.0"
+        "phpunit/phpunit": "^9.0"
     },
     "autoload": {
         "psr-4": {