[skip ci] UPGRADING: mention SID deprecation (#16238)

Refs: https://wiki.php.net/rfc/deprecate-get-post-sessions / PR 13578

Co-authored-by: jrfnl <jrfnl@users.noreply.github.com>

Author: jrfnl

UPGRADING

@@ -581,7 +581,7 @@ PHP 8.4 UPGRADE NOTES
     RFC: https://wiki.php.net/rfc/deprecations_php_8_4#sessionsid_length_and_sessionsid_bits_per_character
   . Changing the INI settings session.use_only_cookies, session.use_trans_sid,
     session.trans_sid_tags, session.trans_sid_hosts, and session.referer_check
-    is deprecated.
+    is deprecated. The SID constant is also deprecated.
     RFC: https://wiki.php.net/rfc/deprecate-get-post-sessions
 
 - SOAP: