Update Testbench for L8 support

composer.json

@@ -38,7 +38,7 @@
     "dms/phpunit-arraysubset-asserts": "^0.1.0",
     "laravel/lumen-framework": "^5.8|^6.0|^7.0|^8.0",
     "league/fractal": "^0.19.0",
-    "orchestra/testbench": "^3.7|^4.0|^5.0",
+    "orchestra/testbench": "^3.7|^4.0|^5.0|^6.0",
     "phpstan/phpstan": "^0.12.19",
     "phpunit/phpunit": "^8.0|^9.0"
   },