sea: update stability index

The design is relatively stable now and it's more suitable to
describe it as being "in active developement".

PR-URL: #51774
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Moshe Atlow <moshe@atlow.co.il>
Reviewed-By: Debadree Chatterjee <debadree333@gmail.com>
Reviewed-By: Yagiz Nizipli <yagiz.nizipli@sentry.io>

doc/api/single-executable-applications.md

@@ -15,7 +15,7 @@ changes:
     description: Added support for "useCodeCache".
 -->
 
-> Stability: 1 - Experimental: This feature is being designed and will change.
+> Stability: 1.1 - Active development
 
 <!-- source_link=src/node_sea.cc -->