reduce preferred version to match the rest of the modules

Author: Jacek Krysztofik

modules/webhook/versions.tf

@@ -9,7 +9,7 @@ terraform {
 
     null = {
       source  = "hashicorp/null"
-      version = "~> 3.2"
+      version = "~> 3"
     }
   }
 }