test/test-server: Include gcal-utils header

This is a followup to 008b914f9e
in order to use gcal_create_soup_session.

The test was disabled and the breakage sneak through.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-calendar/-/merge_requests/668>

tests/test-server.c

@@ -22,6 +22,7 @@
 #include <libedataserver/libedataserver.h>
 
 #include "gcal-simple-server.h"
+#include "gcal-utils.h"
 
 static GcalSimpleServer*
 init_server (void)