t5605: fix test for cloning from a different user

This test currently passes, but for the wrong reason. The repo_is_hardlinked function expects a .git directory or a bare repository and currently fails because it cannot find the objects directory. One solution is to use the --bare argument, but then --show-toplevel won't work. We could change that, but there's no need to, so just add the missing .git directory. In addition, use the built-in negation functionality of test_grep to avoid mishandling real errors (such as a missing file) and, as a final fix, remove the extra newline. Reported-by: SZEDER Gábor <szeder.dev@gmail.com> Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>