Add remaining missing return types to safe methods

Author: wouterj

CompiledRoute.php

@@ -86,7 +86,7 @@ public function __unserialize(array $data): void
     /**
      * @internal
      */
-    final public function unserialize(string $serialized)
+    final public function unserialize(string $serialized): void
     {
         $this->__unserialize(unserialize($serialized, ['allowed_classes' => false]));
     }

Route.php

@@ -102,7 +102,7 @@ public function __unserialize(array $data): void
     /**
      * @internal
      */
-    final public function unserialize(string $serialized)
+    final public function unserialize(string $serialized): void
     {
         $this->__unserialize(unserialize($serialized));
     }