support installing phpunit 8 or 9 if needed

Athlon1600 · Athlon1600 · commit aa775ae654e4 · 2023-10-07T18:19:38.000-05:00
diff --git a/composer.json b/composer.json
@@ -8,7 +8,7 @@
     "ext-json": "*"
   },
   "require-dev": {
-    "phpunit/phpunit": "^7.0"
+    "phpunit/phpunit": "^7.0 || ^8.0 || ^9.0"
   },
   "autoload": {
     "psr-4": {
