Fix locale-specific time

In zpool status -t, scrub date/time is reported using the C locale,
while trim time is reported using the current one. This is inconsistent.
This patch fixes that.

Reviewed-by: Tino Reichardt <milky-zfs@mcmilk.de>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Maxim Filimonov <che@bein.link>
Closes #15878
Closes #15879