Number SE 0487-extensible-enums.md (#2862)

Author: airspeedswift

proposals/NNNN-extensible-enums.md renamed to proposals/0487-extensible-enums.md

@@ -1,6 +1,6 @@
 # Extensible enums
 
-* Proposal: [SE-NNNN](NNNN-extensible-enums.md)
+* Proposal: [SE-0487](0487-extensible-enums.md)
 * Authors: [Pavel Yaskevich](https://github.com/xedin), [Franz Busch](https://github.com/FranzBusch), [Cory Benfield](https://github.com/lukasa)
 * Review Manager: [Ben Cohen](https://github.com/airspeedswift)
 * Status: **In active review (May 25—Jun 5, 2025)**