fix: don't crash reading contributors when not logged into GitHub

[JoshuaKGoldberg]

PR Checklist

• Addresses an existing open issue: fixes 🐛 Bug: Crashes if run without a logged-in gh user #1971
• That issue was marked as status: accepting prs
• Steps in CONTRIBUTING.md were taken

Overview

The GET /user result can be undefined if the user isn't logged in.

🎁

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.85%. Comparing base (e6402c6) to head (b2bd7d1).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1972   +/-   ##
=======================================
  Coverage   94.85%   94.85%           
=======================================
  Files          91       91           
  Lines        3655     3656    +1     
  Branches      214      215    +1     
=======================================
+ Hits         3467     3468    +1     
  Misses        188      188           

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[github-actions]

🎉 This is included in version v2.4.2 🎉

The release is available on:

• GitHub releases
• npm package (@latest dist-tag)

Cheers! 📦🚀