doc: migration-guide: 4.1: rename gpio-stepper compatible

add entry in migration guide 4.1 about renaming of compatible from
zephyr,gpio-steppers to zephyr,gpio-stepper

Signed-off-by: Jilay Pandya <[email protected]>

Author: jilaypandya

doc/releases/migration-guide-4.1.rst

@@ -66,6 +66,11 @@ Sensors
 Serial
 ======
 
+Stepper
+=======
+
+  * Renamed the ``compatible`` from ``zephyr,gpio-steppers`` to :dtcompatible:`zephyr,gpio-stepper`.
+
 Regulator
 =========