feat: bump CI version of Node to 20

[JoshuaKGoldberg]

PR Checklist

• Addresses an existing open issue: fixes 🛠 Tooling: Bump Node version used in CI from 18 to 20 #1204
• That issue was marked as status: accepting prs
• Steps in CONTRIBUTING.md were taken

Overview

Swaps the number from 18 to 20. Straightforward.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (4a58d10) 94.82% compared to head (c24eb5c) 94.82%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1233   +/-   ##
=======================================
  Coverage   94.82%   94.82%           
=======================================
  Files         104      104           
  Lines        5815     5815           
  Branches      491      491           
=======================================
  Hits         5514     5514           
  Misses        300      300           
  Partials        1        1           

Flag	Coverage Δ
create	70.04% <100.00%> (ø)
initialize	42.25% <0.00%> (ø)
migrate	69.76% <100.00%> (ø)
unit	75.53% <100.00%> (ø)

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[github-actions]

🎉 This is included in version v1.54.0 🎉

The release is available on:

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

Cheers! 📦🚀