Add remaining missing return types to safe methods

Author: wouterj

Authentication/Token/AbstractToken.php

@@ -172,7 +172,7 @@ final public function serialize(): string
     /**
      * @internal
      */
-    final public function unserialize(string $serialized)
+    final public function unserialize(string $serialized): void
     {
         $this->__unserialize(unserialize($serialized));
     }