fix: remove duplicate import in cache-metrics test

Remove duplicate getInstanceCacheMetrics import that was causing TypeScript linting error

🤖 Generated with Claude Code

Co-Authored-By: Claude <noreply@anthropic.com>

tests/unit/monitoring/cache-metrics.test.ts

@@ -4,7 +4,6 @@
 
 import { describe, it, expect, beforeEach, vi, afterEach } from 'vitest';
 import {
-  getInstanceCacheMetrics,
   getInstanceCacheMetrics,
   getN8nApiClient,
   clearInstanceCache