Use VTU in filters specs

What does this MR do?

This refactors ee/spec/frontend/security_dashboard/components/filters_spec.js to use Vue Test Utils' mount() helper instead of mountComponentWithStore().

Screenshots

This is all backstage.

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• [-] Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Closes #218451 (closed)