docs: clarify that validation is skipped for presets as well

Author: Abdalrhman-Almarakeby

docs/src/app/docs/customization/page.mdx

@@ -16,6 +16,8 @@ Skipping validation is not encouraged and will lead to your types and runtime va
 
 </Callout>
 
+When enabled, validation will be skipped for both your environment variables and any [extended presets](#extending-presets).
+
 ```ts title="src/env.ts"
 import { createEnv } from "@t3-oss/env-core";