Resolve "Migrate spec/javascripts/vue_shared/components/file_icon_spec.js to Jest"

What does this MR do?

Issue: https://gitlab.com/gitlab-org/gitlab-ce/issues/66660

Refactors file_icon_spec.js tests from karma to jest + vue-test-utils

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry for user-facing changes, or community contribution. Check the link for other scenarios.
• [-] Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content