test-fuse.sh: set TZ=UTC for ls dates

Thanks to Mark J Hewitt <mjh@idnet.com> and Scott Sugar
<scottsugar@outlook.com> for reporting the problem, and Patrick
Rouleau <prouleau72@gmail.com> for helping test the solution.

Signed-off-by: Rob Browning <rlb@defaultvalue.org>
Tested-by: Rob Browning <rlb@defaultvalue.org>