docs: tweak migration guide

[duposyl]

Fixed command line to use the apply changes. Also added testing when validating the changes.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.69%. Comparing base (c997de6) to head (255f3f0).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #791   +/-   ##
=======================================
  Coverage   89.69%   89.69%           
=======================================
  Files          47       47           
  Lines      187134   187134           
  Branches     1335     1335           
=======================================
  Hits       167842   167842           
  Misses      18897    18897           
  Partials      395      395           

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[jwinkle8]

Looks good to me. Thanks for catching this @duposyl.