chore: Add @metamask-previews/* to NPM age gate exceptions

[Mrtenz]

We sometimes use @metamask-previews/* to use preview builds for testing certain features. These will usually not be 3 days old, so can't be installed without an exception.

---

Note

Adds @metamask-previews/* to npmPreapprovedPackages in .yarnrc.yml to bypass the 3-day NPM minimal age gate.

^{Written by Cursor Bugbot for commit 571c068. This will update automatically on new commits. Configure here.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.29%. Comparing base (18b335e) to head (571c068).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3699   +/-   ##
=======================================
  Coverage   98.29%   98.29%           
=======================================
  Files         417      417           
  Lines       11925    11925           
  Branches     1851     1851           
=======================================
  Hits        11722    11722           
  Misses        203      203           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.