Fix nesting of array structure.

src/Plugin/Block/FacetBlock.php

@@ -102,9 +102,10 @@ class FacetBlock extends BlockBase implements ContainerFactoryPluginInterface {
         '#attributes' => [
           'class' => ['block-facet__wrapper'],
         ],
-        $facet_build,
       ];
 
+      $build = array_merge($facet_build, $build);
+
       // Add css classes.
       if (!empty($facet_build[0]['#attributes']['class'])) {
         $css_classes = $facet_build[0]['#attributes']['class'];