Fix iot_class

Author: ludeeus

custom_components/healthchecksio/manifest.json

@@ -3,7 +3,7 @@
   "name": "Healthchecks.io",
   "documentation": "https://github.com/custom-components/healthchecksio",
   "issue_tracker": "https://github.com/custom-components/healthchecksio/issues",
-  "iot_class": "cloud_pull",
+  "iot_class": "cloud_polling",
   "config_flow": true,
   "codeowners": [
     "@ludeeus"