build: Support libical 4

libical 4 changed several APIs used by GNOME Calendar:

 - libical-glib now provides autoptr cleanup for ICalTime, so only
   define it ourselves for older versions.
 - i_cal_recurrence_get/set_by_day() were removed in favor of the
   dynamically sized by-rule arrays; add local helpers on top of
   i_cal_recurrence_get/set_by().
 - i_cal_errno_return() was renamed to i_cal_error_icalerrno().

Also make the create-tzid event test independent of line folding,
which differs between libical versions.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/utils/gcal-utils.h

@@ -60,7 +60,9 @@ typedef void (*GcalAskRecurrenceCallback) (GcalEvent             *event,
                                            GcalRecurrenceModType  modtype,
                                            gpointer               user_data);
 
+#if ICAL_MAJOR_VERSION < 4
 G_DEFINE_AUTOPTR_CLEANUP_FUNC (ICalTime, g_object_unref)
+#endif
 
 gchar*               gcal_util_get_weekday                       (gint                i);