fix: 1954f8-related issue #2

mkdir operation was passing user instead if actor. I really think I
changed this already; getting a crazy deja-vu feeling about it. Maybe a
commit was lost somewhere along the road, but not sure.

src/backend/src/routers/filesystem_api/mkdir.js

@@ -80,7 +80,7 @@ module.exports = eggspress('/mkdir', {
             req.body.create_missing_ancestors ??
             req.body.create_missing_parents
         ),
-        user: req.user,
+        actor: req.actor,
         shortcut_to: req.values.shortcut_to,
     });