t/helper: allow chmtime to print verbosely without modifying mtime
The `test-tool chmtime` helper allows us to both read and modify the
modification time of files. But while it is possible to only read the
mtimes of a file via `--get`, it is not possible to read the mtimes
and report them together with their respective file paths via the
`--verbose` flag without also modifying the mtime at the same time.
Fix this so that it is possible to call `test-tool chmtime --verbose
<files>...` without modifying any mtimes.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>