BUGFIX: Set correct siteNode in WorkspaceController

This fixes a merge error introduced with fa38119

We check `$ancestor` to be of nodeType `Neos.Neos:Site` so this is the correct value for `$siteNode`.

Relates: #4588

Neos.Neos/Classes/Controller/Module/Management/WorkspacesController.php

@@ -792,7 +792,7 @@ protected function computeSiteChanges(Workspace $selectedWorkspace, ContentRepos
                         }
                     }
                     if ($this->getNodeType($ancestor)->isOfType(NodeTypeNameFactory::NAME_SITE)) {
-                        $siteNode = $documentNode;
+                        $siteNode = $ancestor;
                     }
                 }