Correct the RustyNES core license (MIT/Apache -> GPL-3.0-or-later)

RustyNES relicensed in its v2.2.9 release (2026-08-04). This page predates
that change and still lists the old terms.

Author: doublegate

docs/library/rustynes.md

@@ -14,7 +14,7 @@ The RustyNES core has been authored by
 
 The RustyNES core is licensed under
 
-- MIT OR Apache-2.0
+- GPL-3.0-or-later
 
 A summary of the licenses behind RetroArch and its cores can be found [here](../development/licenses.md).