Add migration guide for `shadow_pass` split (#24262)

# Objective

- Fixes #24256 

## Solution

- Adds the migration guide

## Testing

- CI will let me know if it’s formatted incorrectly

Kevin Chen committed 3mo ago

0725f2653329e0f3076f67266f10398057093d05

Parent: 606dac7

Committed by GitHub <noreply@github.com> on 5/12/2026, 11:00:10 PM