Issue #3240194 by andypost:...

Issue #3240194 by andypost: \Drupal\KernelTests\Core\Routing\RouteProviderTest::testDuplicateRoutePaths can cause deprecations on PHP 8.1

core/tests/Drupal/KernelTests/Core/Routing/RouteProviderTest.php

@@ -288,7 +288,7 @@ public function testDuplicateRoutePaths($path, $number, $expected_route_name = N
     $routes = $provider->getRouteCollectionForRequest($request);
     $this->assertCount($number, $routes, 'The correct number of routes was found.');
     if ($expected_route_name) {
-      $route_name = key(current($routes));
+      $route_name = $routes->getIterator()->key();
       $this->assertEquals($expected_route_name, $route_name, 'The expected route name was found.');
     }
   }