fix: reset codecov-action back to v3

[JoshuaKGoldberg]

PR Checklist

• Addresses an existing open issue: fixes 🐛 Bug: Codecov reports not updating since codecov-action updated to v4 #1303
• That issue was marked as status: accepting prs
• Steps in CONTRIBUTING.md were taken

Overview

codecov/codecov-action#1292 & codecov/feedback#273 make me not want to deal with this token stuff until it's all resolved.

Things were working fine before, and I really don't want to add a third token requirement to repos made with create-typescript-app.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (2ea1c18) 94.79% compared to head (8641038) 95.88%.
Report is 18 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1304      +/-   ##
==========================================
+ Coverage   94.79%   95.88%   +1.09%     
==========================================
  Files         103      104       +1     
  Lines        5781     5788       +7     
  Branches      490      490              
==========================================
+ Hits         5480     5550      +70     
+ Misses        300      237      -63     
  Partials        1        1              

Flag	Coverage Δ
create	69.99% <87.03%> (+0.05%)	⬆️
initialize	42.54% <85.80%> (+0.14%)	⬆️
migrate	69.90% <87.03%> (+0.07%)	⬆️
unit	76.82% <100.00%> (+1.15%)	⬆️

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[github-actions]

🎉 This is included in version v1.57.4 🎉

The release is available on:

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

Cheers! 📦🚀