[Regression] Attachments cannot be uploaded with old API

[V3L0C1T13S]

Where does this issue apply? (REST api, cdn, gateway, voice server, remote auth)
REST api

Expected behavior
Attachments should upload properly using the old attachments API

Actual behavior
Attachments do not upload with the old API

Screenshots
Esmbot running via Reflectcord failing to upload attachments

[V3L0C1T13S]

Fixed in bc0e2e4