t7501.8: feed a meaningful command

t7501.8: feed a meaningful command

The command expects "git commit --interactive <path>" to fail because you
cannot (yet) limit "commit --interactive" with a pathspec, but even if the
command allowed to take <path>, the test would have failed as saying just
7:quit would leave the index the same as the current commit, leading to an
attempt to create an empty commit that would fail without --allow-empty.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>