time-stamp: update support for time zone numeric offset

* time-stamp.el (time-stamp-string-preprocess): Change new format for
numeric time zone from %:z to %5z to match format-time-string better.
(time-stamp-format): Document support for numeric time zone.
See discussion in bug#32931.

* NEWS: Mention time-stamp-format %5z.
1 job for master in 90 minutes and 1 second (queued for 3 seconds)
Status Job ID Name Coverage
  Test
failed #4208
test-all

01:30:01

 
Name Stage Failure
failed
test-all Test The script exceeded the maximum execution time set for the job
  GEN      lisp/cedet/semantic-utest.log
ELC lisp/cedet/srecode-utest-getset.elc
GEN lisp/cedet/srecode-utest-getset.log
ELC lisp/cedet/srecode-utest-template.elc
GEN lisp/cedet/srecode-utest-template.log
ELC lisp/char-fold-tests.elc
GEN lisp/char-fold-tests.log
Pulling docker image gitlab/gitlab-runner-helper:x86_64-d0b76032 ...
ERROR: Job failed: execution took longer than 1h30m0s seconds