Add missing return annotations on magic methods

Author: nicolas-grekas

Loader/Configurator/ReferenceConfigurator.php

@@ -59,6 +59,9 @@ final public function ignoreOnUninitialized(): self
         return $this;
     }
 
+    /**
+     * @return string
+     */
     public function __toString()
     {
         return $this->id;

Variable.php

@@ -33,6 +33,9 @@ public function __construct(string $name)
         $this->name = $name;
     }
 
+    /**
+     * @return string
+     */
     public function __toString()
     {
         return $this->name;