doc: report proper return type on url.format

Signed-off-by: Brian Muenzenmeyer <brian.muenzenmeyer@gmail.com>
PR-URL: #64806
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: René <contact.9a5d6388@renegade334.me.uk>

Author: bmuenzenmeyer

doc/api/url.md

@@ -1741,6 +1741,7 @@ changes:
 
 * `urlObject` {Object} A URL object (as returned by `url.parse()` or
   constructed otherwise).
+* Returns: {string}
 
 The `url.format()` method returns a formatted URL string derived from
 `urlObject`.
@@ -1836,6 +1837,7 @@ changes:
 
 * `urlString` {string} A string that will be passed to `url.parse()` and then
   formatted.
+* Returns: {string}
 
 `url.format(urlString)` is shorthand for `url.format(url.parse(urlString))`.