Update dependency guzzlehttp/guzzle to v7.15.0

Author: renovate[bot]

composer.json

@@ -36,7 +36,7 @@
     "symfony/polyfill-php80": "1.37.0",
     "erusev/parsedown": "1.8.0",
     "mexitek/phpcolors": "dev-master",
-    "guzzlehttp/guzzle": "7.14.2",
+    "guzzlehttp/guzzle": "7.15.0",
     "instituteweb/composer-scripts": "1.1.0"
   },
   "autoload": {