Fix beta breadcrumb

After introducing Bootstrap 4.5.0, the breadcrumb icons weren't aligned
anymore. Because `breadcrumb-item` now are flex.
Since we modified the breadcrumb, we changed from `display: flex` to
`display: block`, in order to have the previous behaviour.

src/api/app/assets/stylesheets/webui/responsive_ux/_layout.scss

@@ -45,7 +45,10 @@
 .breadcrumb {
   padding-bottom: 0;
   @extend .mt-2;
-  .breadcrumb-item { line-height: 1.5rem; }
+  .breadcrumb-item {
+    display: block;
+    line-height: 1.5rem;
+  }
   .breadcrumb-item::after {
     display: inline-block;
     padding: 0 0.5rem 0 0.25rem;