testsuite: use exitcode 77 for skipped tests

Using 77 is a de-facto standard for skipped tests that both autotools
and meson support OOTB. Use that instead of EXIT_SUCCESS aka 0.

Semi-recently we removed the only skip = true tests, although with more
tests incoming we're need bound to have a few users.

Signed-off-by: Emil Velikov <[email protected]>
Link: #246
Signed-off-by: Lucas De Marchi <[email protected]>

testsuite/testsuite.c

@@ -1018,7 +1018,7 @@ static inline int test_run_parent(const struct test *t, int fdout[2], int fderr[
 	if (t->skip) {
 		LOG("%sSKIPPED%s: %s\n", ANSI_HIGHLIGHT_YELLOW_ON, ANSI_HIGHLIGHT_OFF,
 		    t->name);
-		err = EXIT_SUCCESS;
+		err = 77;
 		goto exit;
 	}