fix: Increase minimum required PHP version to 8.1

composer.json

@@ -12,7 +12,7 @@
     "homepage": "https://git.zsinfo.nl/Zandor300/solvari-php-sdk",
     "license": "Apache-2.0",
     "require": {
-        "php": ">=7.3.0",
+        "php": ">=8.1.0",
         "ext-json": "*",
         "ext-curl": "*"
     },