Fix import that was resulting in a depcheck error (#20383)

An import was introduced in #20125 that was broken. It was importing
from `app/` instead of using a relative import. This was causing the
CI "depcheck" job to fail. The import has been updated to use a
relative path.

app/scripts/lib/ppom/ppom-middleware.ts

@@ -5,7 +5,7 @@ import {
   BlockaidReason,
   BlockaidResultType,
 } from '../../../../shared/constants/security-provider';
-import PreferencesController from 'app/scripts/controllers/preferences';
+import PreferencesController from '../../controllers/preferences';
 
 const { sentry } = global as any;