Issue #3471485 by pdureau: Fix ComponentElementAlter::processAttributes()

src/Element/ComponentElementAlter.php

@@ -71,8 +71,8 @@ class ComponentElementAlter implements TrustedCallbackInterface {
       return $element;
     }
     $attributes = new Attribute($element["#attributes"]);
-    if (isset($element["#props"]["#attributes"])) {
-      $attributes = (new Attribute($element["#props"]["#attributes"]))->merge($attributes);
+    if (isset($element["#props"]["attributes"])) {
+      $attributes = (new Attribute($element["#props"]["attributes"]))->merge($attributes);
     }
     $element["#props"]["attributes"] = $attributes;
     return $element;