t7700: do not use "touch" unnecessarily
Some versions of touch (such as /usr/ucb/touch on Solaris)
do not know about the "-r" option. This would make sense as
a feature of test-chmtime, but fortunately this fix is even
easier.
The test does not care about the timestamp of the .keep file it
creates at all, only that it exists. For such a use case, with or
without portability issues around "-r", "touch" should not be used
in the first place.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>