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

(cherry picked from commit 428db04)

Original-Signed-off-by: Jilay Pandya <jilay.pandya@outlook.com>
GitOrigin-RevId: 428db04
Cr-Build-Id: 8730847287260936497
Cr-Build-Url: https://cr-buildbucket.appspot.com/build/8730847287260936497
Copybot-Job-Name: zephyr-main-copybot-downstream
Change-Id: I24c151a55458f3c3274f709005c603ea04ac1edb
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/zephyr/+/6035383
Commit-Queue: Tristan Honscheid <honscheid@google.com>
Reviewed-by: Tristan Honscheid <honscheid@google.com>
Tested-by: ChromeOS Prod (Robot) <chromeos-ci-prod@chromeos-bot.iam.gserviceaccount.com>
Tested-by: Tristan Honscheid <honscheid@google.com>

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
 =========