Make artifacts dropdown refetch list on show at 'Pipelines'

At 'Pipelines' artifacts dropdown of any row is fetched only once. Thus
at least two use cases are negatively affected:
- When live-update shifts pipelines_list, view elements are reused, so
  some dropdown may list other pipeline's artifacts after having been
  shown once;
- During a long-time multi-artifact pipeline, one can't poll a dropdown
  for currently available artifacts.
Page refresh solves both cases, but is inconsistent with live-update.
This commit makes dropdown refetch its list on each show.

Issue: https://gitlab.com/gitlab-org/gitlab/-/issues/367955

Changelog: fixed