t6500: use "ls -1" to snapshot ref database state

By doing ls -1 .git/{reftable,refs/heads}, we can capture changes to both
reftable and packed/loose ref storage.

This relies on the fact that git-pack-refs (which we're looking for here)
changes the number (loose/packed storage) and/or names (reftable) files used for
ref storage.

Signed-off-by: Han-Wen Nienhuys <hanwen@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t6500-gc.sh

@@ -241,7 +241,7 @@ test_expect_success 'background auto gc respects lock for all operations' '
 
 	# create a ref whose loose presence we can use to detect a pack-refs run
 	git update-ref refs/heads/should-be-loose HEAD &&
-	test_path_is_file .git/refs/heads/should-be-loose &&
+	(ls -1 .git/refs/heads .git/reftable >expect || true) &&
 
 	# now fake a concurrent gc that holds the lock; we can use our
 	# shell pid so that it looks valid.
@@ -258,7 +258,8 @@ test_expect_success 'background auto gc respects lock for all operations' '
 
 	# our gc should exit zero without doing anything
 	run_and_wait_for_auto_gc &&
-	test_path_is_file .git/refs/heads/should-be-loose
+	(ls -1 .git/refs/heads .git/reftable >actual || true) &&
+	test_cmp expect actual
 '
 
 # DO NOT leave a detached auto gc process running near the end of the