fix(SearchController): replace superglobal with ServerRequest->has()

Replace `empty($_REQUEST['ajax_page_request'])` with
`! $request->has('ajax_page_request')` to use the injected
ServerRequest consistently.

Signed-off-by: Thomas Vincent <thomasvincent@gmail.com>

src/Controllers/Database/SearchController.php

@@ -90,7 +90,7 @@ final readonly class SearchController implements InvocableController
         }
 
         // If we are in an Ajax request, we need to exit after displaying all the HTML
-        if ($request->isAjax() && empty($_REQUEST['ajax_page_request'])) {
+        if ($request->isAjax() && ! $request->has('ajax_page_request')) {
             return $this->response->response();
         }