t/helper/test-dump-split-index: initialize git repository

In this test helper, we read the index.  In order to have the proper
hash algorithm set up, we must call setup_git_directory.  Do so, so that
the test works when extensions.objectFormat is set.

Signed-off-by: brian m. carlson <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: bk2204

t/helper/test-dump-split-index.c

@@ -13,6 +13,8 @@ int cmd__dump_split_index(int ac, const char **av)
 	struct split_index *si;
 	int i;
 
+	setup_git_directory();
+
 	do_read_index(&the_index, av[1], 1);
 	printf("own %s\n", oid_to_hex(&the_index.oid));
 	si = the_index.split_index;