Issue #3351162 fix: Undefined array key when placing blocks in lbb when default language is not english

Commit 10620a91 introduced and error caused by an undefined array key when using the “Place Block” button to add a block to a category in /admin/config/content/layout-builder-browser if a language different than english was selected as the site default language.

Closes #3351162

src/Form/BlockForm.php

@@ -47,9 +47,12 @@ class BlockForm extends EntityForm {
     $block_provider_map = [];
 
     foreach ($definitions as $id => $definition) {
-      $category_id = $category_label = $definition['category'];
       if ($definition['category'] instanceof TranslatableMarkup) {
-        $category_id = $category_label = $definition['category']->render();
+        $category_id = $definition["category"]->getUntranslatedString();
+        $category_label = $definition["category"]->render();
+      }
+      else {
+        $category_id = $category_label = $definition['category'];
       }
 
       $blocks[$category_id][$id] = $definition['admin_label'];