t/lib-submodule-update.sh: fix test ignoring ignored files in submodules

It turns out that the test replacing a submodule with a file with the submodule containing an ignored file is incorrectly titled, because the test put the file in place, but never ignored that file. When having an untracked file Instead of an ignored file in the submodule, git should refuse to remove the submodule, but that is a bug in the implementation of recursing into submodules, such that the test just passed, removing the untracked file. Fix the test first; in a later patch we'll fix gits behavior, that will make sure untracked files are not deleted. Signed-off-by: Stefan Beller <sbeller@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>