test: append, not insert the suites

list_append() came later than list_insert() and there's an argument to
be made that tests added later should be run first since they're less
likely to succeed. But it's a lot harder to read test logs when they are
in reverse order, and with the TEST_COLLECTION() macro the order of the
test suite is not obvious anyway.

Part-of: <https://gitlab.freedesktop.org/libinput/libinput/-/merge_requests/1067>

test/litest.c

@@ -4855,7 +4855,7 @@ setup_tests(void)
 		s->name = safe_strdup(c->name);
 
 		list_init(&s->tests);
-		list_insert(&all_test_suites, &s->node);
+		list_append(&all_test_suites, &s->node);
 
 		current_suite = s;
 		c->setup();