Add missing return types to interfaces

Author: derrabus

Tests/Fixtures/ContainerAwareFixture.php

@@ -18,14 +18,14 @@
 
 class ContainerAwareFixture implements FixtureInterface, ContainerAwareInterface
 {
-    public $container;
+    public ?ContainerInterface $container = null;
 
-    public function setContainer(?ContainerInterface $container)
+    public function setContainer(?ContainerInterface $container): void
     {
         $this->container = $container;
     }
 
-    public function load(ObjectManager $manager)
+    public function load(ObjectManager $manager): void
     {
     }
 }