[skip ci] 8.4 | UPGRADING: add missing constant

Ref: 564914a#diff-c5961ea04ab805b0059964fac68d6e159095a4b56aaaded0b1b941b8768c0f52

Author: jrfnl

UPGRADING

@@ -961,6 +961,9 @@ PHP 8.4 UPGRADE NOTES
   . P_SID (NetBSD/FreeBSD only).
   . P_JAILID (FreeBSD only).
 
+- PgSQL:
+  . PGSQL_TUPLES_CHUNK
+
 - Sockets:
   . SO_EXCLUSIVEADDRUSE (Windows only).
   . SOCK_CONN_DGRAM (NetBSD only).