doc: improve doc for http.ServerResponse inheritance

Document that `http.ServerResponse` inherits from
`http.OutgoingMessage`.

PR-URL: #42693
Reviewed-By: Rich Trott <[email protected]>
Reviewed-By: Darshan Sen <[email protected]>
Reviewed-By: Matteo Collina <[email protected]>
Reviewed-By: Mestery <[email protected]>
Reviewed-By: Akhil Marsonya <[email protected]>
Reviewed-By: Ricky Zhou <[email protected]>
Reviewed-By: James M Snell <[email protected]>

doc/api/http.md

@@ -1497,7 +1497,7 @@ affects new connections to the server, not any existing connections.
 added: v0.1.17
 -->
 
-* Extends: {Stream}
+* Extends: {http.OutgoingMessage}
 
 This object is created internally by an HTTP server, not by the user. It is
 passed as the second parameter to the [`'request'`][] event.