Add IMAP resource to object conversion to UPGRADING

Author: Girgias

UPGRADING

@@ -23,6 +23,10 @@ PHP 8.1 UPGRADE NOTES
   . The fileinfo functions now accept and return, respectively, finfo objects
     instead of resources.
 
+- IMAP:
+  . The IMAP functions now accept and return, respectively, IMAPConnection objects
+    instead of resources.
+
 - MySQLi:
   . mysqli_fetch_fields() and mysqli_fetch_field_direct() will now always return
     zero for max_length. You can compute this information by iterating over the