fix: Prefer s3-PUBLIC remote for validating remote content

[effigies]

@nellh The validator defaults to the most recent S3 remote, which is probably going to be the S3-BACKUP, significantly slowing down (and making more expensive) validation.

I suspect this is the root cause of #3671.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 45.03%. Comparing base (07b085c) to head (35fae1a).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3672      +/-   ##
==========================================
+ Coverage   43.00%   45.03%   +2.02%     
==========================================
  Files         636      636              
  Lines       33909    33918       +9     
  Branches     1516     1595      +79     
==========================================
+ Hits        14583    15274     +691     
+ Misses      19187    18515     -672     
+ Partials      139      129      -10     

☔ 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.