Silence a warning from psalm with explanation

Signed-off-by: Côme Chilliet <come.chilliet@nextcloud.com>

Author: come-nc

lib/private/Files/Storage/Local.php

@@ -617,6 +617,7 @@ public function moveFromStorage(IStorage $sourceStorage, $sourceInternalPath, $t
 	}
 
 	public function writeStream(string $path, $stream, int $size = null): int {
+		/** @var int|false $result We consider here that returned size will never be a float because we write less than 4GB */
 		$result = $this->file_put_contents($path, $stream);
 		if (is_resource($stream)) {
 			fclose($stream);