Bugfix: Show timezone location in `snapshots` output

With restic 0.19.0, the `snapshots` command printed the current timezone when
listing snapshots. However, that timezone label might change during the year,
for example with daylight saving time. Restic now prints a more consistent and
shorter version of the text.

https://github.com/restic/restic/pull/21876
https://forum.restic.net/t/possible-bug-in-timezone-naming/10867
