Fix migration guide links for version updates

[aymericzip]

Updated migration guide links to point to the correct markdown files for versions 2.0, 3.0, and 4.0.

• <- Keep this line and put an x between the brackts.

Description

Linked Issues

fixes #

Additional context

[netlify]

❌ Deploy Preview for shiki-next failed.

Name	Link
🔨 Latest commit	77f2204
🔍 Latest deploy log	https://app.netlify.com/projects/shiki-next/deploys/69aca16d17cd7e00087eecda

[netlify]

❌ Deploy Preview for shiki-matsu failed.

Name	Link
🔨 Latest commit	77f2204
🔍 Latest deploy log	https://app.netlify.com/projects/shiki-matsu/deploys/69aca16dc06827000820003a

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.53%. Comparing base (69bec64) to head (77f2204).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1260   +/-   ##
=======================================
  Coverage   89.53%   89.53%           
=======================================
  Files          79       79           
  Lines        3479     3479           
  Branches     1009     1007    -2     
=======================================
  Hits         3115     3115           
  Misses        328      328           
  Partials       36       36           

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[aymericzip]

canceling,

fix github doc but will break website