doc: unlock module

Update documentation for `module` to reflect stability index 2 (Stable)
rather than 3 (Locked).

PR-URL: #11661
Ref: #11200
Reviewed-By: Anna Henningsen <[email protected]>
Reviewed-By: Sam Roberts <[email protected]>
Reviewed-By: Gibson Fahnestock <[email protected]>
Reviewed-By: Michael Dawson <[email protected]>
Reviewed-By: Michaël Zasso <[email protected]>
Reviewed-By: Сковорода Никита Андреевич <[email protected]>
Reviewed-By: James M Snell <[email protected]>

doc/api/modules.md

@@ -1,6 +1,6 @@
 # Modules
 
-> Stability: 3 - Locked
+> Stability: 2 - Stable
 
 <!--name=module-->