add @since for COMPACT_LAYOUT

Change-Id: I4b7f918e846ea1d220b9df2be5bc0b39d1f22f7d
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/151086
Tested-by: Jenkins
Reviewed-by: Dennis Francis <dennis.francis@collabora.com>

offapi/com/sun/star/sheet/DataPilotFieldLayoutMode.idl

@@ -68,6 +68,8 @@ constants DataPilotFieldLayoutMode
         the subtotals take up more than one row (manually selected, or because there
         are several data fields), they are always shown below the item's data,
         regardless of the setting.</p>
+
+        @since LibreOffice 7.6
      */
 
     const long COMPACT_LAYOUT = 3;