Refs #24104 -- Added missing release notes

Forwardport of 3d4a8261 from stable/1.7.x

docs/releases/1.7.4.txt

@@ -20,3 +20,7 @@ Bugfixes
 
 * Prevented the ``static.serve`` view from producing ``ResourceWarning``\s in
   certain circumstances (security fix regression, :ticket:`24193`).
+
+* Fixed schema check for ManyToManyField to look for internal type instead
+  of checking class instance, so you can write custom m2m-like fields with the
+  same behavior. (:ticket:`24104`).