[skip ci] 8.4 | UPGRADING: add missing entry for DBA resource to object migration

Ref: 14329

P.S.: looks like 14282 also doesn't have a mention, but that PR doesn't appear to have an impact on userland - maybe a NEWS entry ?

UPGRADING

@@ -38,6 +38,11 @@ PHP 8.4 UPGRADE NOTES
     readonly initialization, and was an oversight in the "readonly
     reinitialization during cloning" implementation.
 
+- DBA:
+  . dba_open() and dba_popen() will now return a Dba\Connection
+    object rather than a resource. Return value checks using is_resource()
+    should be replaced with checks for `false`.
+
 - DOM:
   . Added DOMNode::compareDocumentPosition() and DOMNode::DOCUMENT_POSITION_*
     constants.