Improves the empty state when artifacts fail to load

What does this MR do and why?

Once a pipeline completes, a user can build and download artifacts. When there are none to show and there is an error loading artifacts, two errors are placed on top of each other. This MR is to resolve that issue in two places:

/workspace/gitlab/app/assets/javascripts/pipelines/components/pipelines_list/pipelines_artifacts.vue
/workspace/gitlab/app/assets/javascripts/pipelines/components/pipelines_list/pipeline_multi_actions.vue

Current behavior

Pipeline widget on MR Page

Pipelines tab on MR Page

Updated behavior

Pipeline widget on MR Page

Pipelines tab on MR Page

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #341314 (closed)