doc: fix typo in example code for util.styleText

Code shows how to style `errorMessage`, but then
only logs out `successMessage` twice. This might
trip people up when copying the code.

PR-URL: #56720
Reviewed-By: Ulises Gascón <ulisesgascongonzalez@gmail.com>
Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Minwoo Jung <nodecorelab@gmail.com>

Author: rmehner

doc/api/util.md

@@ -1964,7 +1964,7 @@ const errorMessage = styleText(
   // Validate if process.stderr has TTY
   { stream: stderr },
 );
-console.error(successMessage);
+console.error(errorMessage);
 ```
 
 ```cjs