Apply simplest fix for breadcrumbs visual regressions in modeladmin

wagtail/contrib/modeladmin/static_src/wagtailmodeladmin/scss/breadcrumbs_page.scss

@@ -1,12 +1,9 @@
 @import '../../../../../../client/scss/settings';
 @import '../../../../../../client/scss/tools';
 
-.breadcrumb {
-  margin: -1.2em 0 2em;
-}
-
-@include media-breakpoint-up(sm) {
+@include media-breakpoint-down(sm) {
   .breadcrumb {
-    margin-top: -1.8em;
+    margin-inline-start: 30px;
+    margin-inline-end: -20px;
   }
 }

wagtail/contrib/modeladmin/templates/modeladmin/includes/header_with_breadcrumb.html

@@ -1,5 +1,4 @@
-{% extends "wagtailadmin/shared/header_with_locale_selector.html" %}
-
-{% block breadcrumb %}
+<div class="nice-padding">
     {% include "modeladmin/includes/breadcrumb.html" %}
-{% endblock %}
+</div>
+{% include "wagtailadmin/shared/header_with_locale_selector.html" %}