Add tentative return type to Directory::current()

Author: arshidkv12

ext/spl/spl_directory.stub.php

@@ -175,7 +175,7 @@ public function rewind(): void {}
     public function key(): string {}
 
     /** @tentative-return-type */
-    public function current(): string|SplFileInfo|FilesystemIterator {}
+    public function current(): string|SplFileInfo|static {}
 
     /** @tentative-return-type */
     public function getFlags(): int {}