t7405: make hash size independent

Use $ZERO_OID instead of hard-coding a fixed size all-zeros object ID.

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

Author: bk2204

t/t7405-submodule-merge.sh

@@ -195,7 +195,7 @@ test_expect_success 'git submodule status should display the merge conflict prop
        url = $TRASH_DIRECTORY/sub
 EOF
        cat >expect <<EOF &&
-U0000000000000000000000000000000000000000 sub
+U$ZERO_OID sub
 EOF
        git submodule status > actual &&
        test_cmp expect actual &&
@@ -214,7 +214,7 @@ test_expect_success 'git submodule status should display the merge conflict prop
        url = $TRASH_DIRECTORY/sub
 EOF
        cat >expect <<EOF &&
-U0000000000000000000000000000000000000000 sub
+U$ZERO_OID sub
 EOF
        git submodule status > actual &&
        test_cmp expect actual &&