ls: --time-style with format string %Z gives timezone offset instead of name

[jfinkels]

Environment: Ubuntu 20.04, uutils main branch (git commit 00d1866), GNU coreutils v8.30

Steps to reproduce:

TZ=UTC0 touch -d '1970-07-08 09:10:11' f
TZ=UTC0 ls -l --time-style="+%Z" f

What happens now: uutils ls shows a numeric offset for the timezone

-rw-rw-r-- 1 jeffrey jeffrey 0 +00:00 f

What I expected to happen: GNU ls shows the timezone name

-rw-rw-r-- 1 jeffrey jeffrey 0 UTC f

Notes: This causes a failure in the GNU test file tests/ls/time-style.sh.

We use the chrono package for time formatting. It seems that they have an open issue about this here chronotope/chrono#288

[jfinkels]

Related to #5164