Fix a signedness problem in glib/tests/collate.c

glib/tests/collate.c:300:17: error: comparison of integer expressions
  of different signedness: ‘gint’ {aka ‘int’} and ‘long unsigned int’

  300 |   for (i = 0; i < G_N_ELEMENTS (test); i++)
      |                 ^

glib/tests/collate.c

@@ -271,7 +271,7 @@ int
 main (int argc, char *argv[])
 {
   gchar *path;
-  gint i;
+  guint i;
   const gchar *locale;
   CollateTest test[3];