Fixed #32069 -- Fixed admin change-form layout on small screens.

Restored flex-wrap CSS declaration to form elements at smallest breakpoint.
This was present since the responsive admin was introduced in dc37e8846eeedc3a9100ca21fdc9d579bc534c89.
Regression in 8ee4bb6ffcb3346c0fa8fb194986fbf9edadc822, where it was accidentally removed.

django/contrib/admin/static/admin/css/responsive.css

@@ -558,6 +558,7 @@ input[type="submit"], button {
     .aligned .form-row,
     .aligned .form-row > div {
         display: flex;
+        flex-wrap: wrap;
         max-width: 100vw;
     }
 

docs/releases/3.1.3.txt

@@ -45,3 +45,6 @@ Bugfixes
   :exc:`RestrictedError.restricted_objects <django.db.models.RestrictedError>`
   attributes returned iterators instead of :py:class:`set` of objects
   (:ticket:`32107`).
+
+* Fixed a regression in Django 3.1.2 that caused incorrect form input layout on
+  small screens in the admin change form view (:ticket:`32069`).