make package installable in PHP 8.0.x (dev mode)

composer.json

@@ -21,7 +21,7 @@
       "GPL-3.0-or-later"
     ],
     "require": {
-        "php": "^7.3 || ^8.0",
+        "php": "^7.3 || ~8.0.3",
         "beberlei/assert": "^3.3",
         "guzzlehttp/guzzle": "^7.4",
         "psr/http-message": "~1.0",
@@ -30,7 +30,7 @@
         "ext-json": "*"
     },
     "require-dev": {
-        "php": "^7.4",
+        "php": "^7.4 || ~8.0.3",
         "phpunit/phpunit" : "^9.5",
         "friendsofphp/php-cs-fixer": "^3.9",
         "phpstan/phpstan": "^1.8"