doc: move dns.promises to stable status

PR-URL: #26592
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>

doc/api/dns.md

@@ -588,7 +588,7 @@ earlier ones time out or result in some other error.
 
 ## DNS Promises API
 
-> Stability: 1 - Experimental
+> Stability: 2 - Stable
 
 The `dns.promises` API provides an alternative set of asynchronous DNS methods
 that return `Promise` objects rather than using callbacks. The API is accessible