docs: change the signature verify warning to emphasize that raw body needs to be used (#384)

Author: sancar

qstash/howto/signature.mdx

@@ -82,8 +82,8 @@ err := receiver.Verify(qstash.VerifyOptions{
 ```
 </CodeGroup>
 
-<Warning>In JavaScript, the body could be presented by an object via the HTTP handler if it is a JSON. Don't forget to convert to string first via JSON.stringify(body)</Warning>
-
+<Warning>Depending on the environment, the body might be parsed into an object by the HTTP handler if it is JSON. 
+Ensure you use the raw body string as is. For example, converting the parsed object back to a string (e.g., JSON.stringify(object)) may cause inconsistencies and result in verification failure.</Warning>
 
 ### Manual verification