Fixed RFC URL

Author: SakiTakamachi

UPGRADING

@@ -53,7 +53,7 @@ PHP 8.4 UPGRADE NOTES
     RFC: https://wiki.php.net/rfc/gmp-final
   . Casting a GMP object to bool changed so that 0 becomes false and everything else
     becomes true.
-    RFC: https://github.com/php/php-src/pull/15151
+    RFC: https://wiki.php.net/rfc/fix_up_bcmath_number_class
 
 - Intl:
   . resourcebundle_get(), ResourceBundle::get(), and accessing offsets on a