[Test Refactor] Refactor unit test duplication in agent_workspaces_list_spec.js

MR: Pending

Description

The following discussion from !137336 (merged) should be addressed:

• @cwoolley-gitlab started a discussion:

  NOTE: This spec is largely a duplication of pages/list_spec.vue, because the functionality is the same.

  I did ensure that the test coverage is the same across both of them (except for the parts of logic that were already not covered by existing tests)

  Some of it should maybe be moved to a new spec for components/common/workspacess_list.vue, but I'm trying to get this MR out for Remote Development GA, so I didn't want to do a significant spec redesign.

  But I'm not sure if that's desirable, as we may want to keep the coverage at as higher-in-the-test-pyramid integration tests rather they trying to test it all at the component level?

  And also we may be redesigning this UI and component, and possibly duplicating it, so they will likely diverge more in the future.

  We can make a follow-up issue in GitLab Agent UI - Improvements for Workspaces a... (&12348) if we want to refactor out to compenent level coverage, and backfill more test coverage.

  I'll leave this thread open for maintainer feedback, and if we are OK with a follow up, can close the thread by creating the follow-up issue.

Acceptance Criteria

• Duplication is removed as explained in the description

Technical Requirements

• See description for details.