downgrade orchestra test bench to 5.x (laravel 7)

add php7.3 requirement

composer.json

@@ -14,10 +14,13 @@
         "Laravel",
         "Enum"
     ],
+    "require": {
+        "php": "^7.3"
+    },
     "require-dev": {
         "phpunit/phpunit": "~9.0",
         "squizlabs/php_codesniffer": "^3.5",
-        "orchestra/testbench": "^6.13",
+        "orchestra/testbench": "^5",
         "slevomat/coding-standard": "^7.0",
         "phpunit/php-code-coverage": "^9.2"
     },
@@ -39,6 +42,9 @@
         }
     },
     "scripts": {
+        "post-autoload-dump": [
+            "@php ./vendor/bin/testbench package:discover --ansi"
+        ],
         "test": "vendor/bin/phpunit"
     }
 }