changes floats to flex on breadcrumbs (#23683)

scss/_breadcrumb.scss

@@ -1,15 +1,14 @@
 .breadcrumb {
+  display: flex;
+  flex-wrap: wrap;
   padding: $breadcrumb-padding-y $breadcrumb-padding-x;
   margin-bottom: $breadcrumb-margin-bottom;
   list-style: none;
   background-color: $breadcrumb-bg;
   @include border-radius($border-radius);
-  @include clearfix;
 }
 
 .breadcrumb-item {
-  float: left;
-
   // The separator between breadcrumbs (by default, a forward-slash: "/")
   + .breadcrumb-item::before {
     display: inline-block; // Suppress underlining of the separator in modern browsers