Fix invalid test-input file

This file generated a libical error complaining

    Can't parse as RECUR value in RRULE property. Removing entire property: FREQ=YEARLY\;UNTIL=123456T123456\;BYSETPOS=-1\,2\,-3\,4\,-5\,6\,-7\,8\,9\,10\,11\,12\,13\,14\,15\,16\,17\,18\,19\,20\,21\,22\,23\,4\,25\,26\,27\,28\,29\,30\,31\,32\,33\,34\,35\,36\,37\,38\,39\,40\,41\,42\,43\,44\,45\,46\,47\,48\,49\,50\,51\,52\,53\,54\;BYSECOND=1\,2\,3\,4\,5\,6\,7\,8\,9\,10\,11\,12\,13\,14\,15\,16\,17\,18\,19\,20\,21\,22\,23\,4\,25\,26

The error makes three of the tests for this file fail.

The issue appears to be that the UNTIL value is invalid; adding two more
digits (allowing it to be parsed as a YYYYMMDD string) fixes the error.
As far as I can tell this error is irrelevant for the affected tests.

Author: tikitu

XbICalendar/XbICalendarTests/TestData/smallcluster.ics

@@ -7,7 +7,7 @@ DTSTART
  :19970714T170000Z
 DTEND:19970715T035959Z
 SUMMARY:Bastille Day Party
-RRULE:FREQ=YEARLY;UNTIL=123456T123456;BYSETPOS=-1,2,-3,4,-5,6,-7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,4,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54;BYSECOND=1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,4,25,26
+RRULE:FREQ=YEARLY;UNTIL=12345678T123456;BYSETPOS=-1,2,-3,4,-5,6,-7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,4,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54;BYSECOND=1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,4,25,26
 END:VEVENT
 END:VCALENDAR
 END:VCALENDAR