Restrict supported PHP versions to >= 8.0.7

This is due to a bug in earlier PHP versions on mixed variance rules.

See https://3v4l.org/Uc6TM.

Fixes #15.

Author: kelunik

composer.json

@@ -30,7 +30,7 @@
         }
     ],
     "require": {
-        "php": ">=8"
+        "php": ">=8.0.7"
     },
     "require-dev": {
         "ext-json": "*",