Add guzzlehttp/psr7 as explicit dev dependency

Author: JaZo

composer.json

@@ -32,6 +32,7 @@
     "require-dev": {
         "friendsofphp/php-cs-fixer": "^3.0",
         "guzzlehttp/guzzle": "^7.3",
+        "guzzlehttp/psr7": "^2.1",
         "phpunit/phpunit": "^9.5"
     },
     "provide": {