Address review feedback

- Actually filter bot reviews (not just comment about it)
- Use core.setFailed() instead of silently swallowing errors
- Remove unused getEffectiveOwners import from detectors.js

.github/scripts/auto-label-pr/detectors.js

@@ -7,7 +7,7 @@ const {
   hasDashboardChanges,
   hasGitHubActionsChanges,
 } = require('../detect-tags');
-const { fetchCodeowners, getEffectiveOwners } = require('../codeowners');
+const { fetchCodeowners } = require('../codeowners');
 
 // Strategy: Merge branch detection
 async function detectMergeBranch(context) {