doc: fix stability text for n-api

While some places list n-api as stable, the reference
in doc/api/addons.md was missed.  This fixes that
instance.

Fixes: #20645
PR-URL: #20659
Reviewed-By: Vse Mozhet Byt <[email protected]>
Reviewed-By: Luigi Pinca <[email protected]>
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: Trivikram Kamat <[email protected]>
Reviewed-By: Anna Henningsen <[email protected]>
Reviewed-By: Tobias Nießen <[email protected]>

Author: mhdawson

doc/api/addons.md

@@ -219,7 +219,7 @@ illustration of how it can be used.
 
 ## N-API
 
-> Stability: 1 - Experimental
+> Stability: 2 - Stable
 
 N-API is an API for building native Addons. It is independent from
 the underlying JavaScript runtime (e.g. V8) and is maintained as part of