Issue #3348960: @todo Add return type when php 7.4 support ends

src/Controller/InstallerController.php

@@ -15,6 +15,7 @@ use Drupal\project_browser\EnabledSourceHandler;
 use Psr\Log\LoggerInterface;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 use Symfony\Component\HttpFoundation\JsonResponse;
+use Symfony\Component\HttpFoundation\RedirectResponse;
 
 /**
  * Defines a controller to install projects via UI.
@@ -261,10 +262,8 @@ class InstallerController extends ControllerBase {
    *
    * @return \Symfony\Component\HttpFoundation\JsonResponse|\Symfony\Component\HttpFoundation\RedirectResponse
    *   Redirects to the main project browser page.
-   *
-   * @todo add return type when php 7.4 support ends.
    */
-  public function unlock() {
+  public function unlock(): JsonResponse|RedirectResponse {
     try {
       // It's possible the unlock url was provided before applying began, but
       // accessed after. This final check ensures a destroy is not attempted