doc: releases: migration-guide-4.4: Fix QSPI title

Add missing = for the QSPI title.

Signed-off-by: Pieter De Gendt <[email protected]>

Author: pdgendt

doc/releases/migration-guide-4.4.rst

@@ -61,7 +61,7 @@ MDIO
   (:github:`99690`).
 
 QSPI
-===
+====
 
 * :dtcompatible:`st,stm32-qspi` compatible nodes configured with ``dual-flash`` property
   now need to also include the ``ssht-enable`` property to reenable sample shifting.