BUG Retain page search state on list view actions (fixes #7648)

The ".action-detail" link behaviour overloads GridField's
showDetailForm() method, which in turn appends any query params
to the URL (including the existing search params).

code/controllers/CMSMain.php

@@ -715,7 +715,7 @@ public function ListViewForm() {
 				}
 			},
 			'getTreeTitle' => function($value, &$item) use($controller) {
-				return '<a class="cms-panel-link" href="' . singleton('CMSPageEditController')->Link('show') . '/' . $item->ID . '">' . $item->TreeTitle . '</a>';
+				return '<a class="action-detail" href="' . singleton('CMSPageEditController')->Link('show') . '/' . $item->ID . '">' . $item->TreeTitle . '</a>';
 			}
 		));