[test] Suggest updating the expectation if ttx matches

https://github.com/harfbuzz/harfbuzz/issues/3089#issuecomment-892208892

test/subset/run-tests.py

diff --git a/test/subset/run-tests.py b/test/subset/run-tests.py
index 0a7453c..93b1d51 100755
--- a/test/subset/run-tests.py
+++ b/test/subset/run-tests.py
@@ -103,7 +103,9 @@
 		sys.stdout.flush ()
 		return fail_test (test, cli_args, 'ttx for expected and actual does not match.')
 
-	return 1
+	return fail_test (test, cli_args, 'hash for expected and actual does not match, '
+	                                  'but the ttx matches. Expected file needs to be updated?')
+
 
 def has_ots ():
 	if not ots_sanitize: