Merge branch '5.4' into 6.0

* 5.4:
  Add missing return types to tests/internal/final methods
  Add type to fix 6.0 build

Author: nicolas-grekas

Tests/Service/ServiceSubscriberTraitTest.php

@@ -42,7 +42,7 @@ public function aParentService(): Service1
     {
     }
 
-    public function setContainer(ContainerInterface $container): ?ContainerInterface
+    public function setContainer(ContainerInterface $container)
     {
         return $container;
     }