fix: use plugin:markdown/recommended-legacy

[JoshuaKGoldberg]

PR Checklist

• Addresses an existing open issue: fixes 🐛 Bug: Generated legacy ESLint config should use plugin:markdown/recommended-legacy #1380
• That issue was marked as status: accepting prs
• Steps in CONTRIBUTING.md were taken

Overview

Switches to the recommended-legacy plugin and bumps eslint-plugin-markdown to the latest version, 4.x.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.89%. Comparing base (0b494fa) to head (98257ad).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1381   +/-   ##
=======================================
  Coverage   95.89%   95.89%           
=======================================
  Files         104      104           
  Lines        5799     5799           
  Branches      500      500           
=======================================
  Hits         5561     5561           
  Misses        237      237           
  Partials        1        1           

Flag	Coverage Δ
create	69.90% <100.00%> (ø)
initialize	42.55% <0.00%> (ø)
migrate	69.82% <100.00%> (ø)
unit	76.93% <100.00%> (ø)

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[github-actions]

🎉 This is included in version v1.57.9 🎉

The release is available on:

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

Cheers! 📦🚀