bootc usr-overlay mounts with improper permissions on composefs backend

I'm not sure if this applies to the ostree backend, but on the composefs backend, when running `bootc usr-overlay`, /usr is mounted in a way that only the root user is allowed to read the files.

<img width="468" height="600" alt="Image" src="https://github.com/user-attachments/assets/98585491-1333-468c-a5cd-1d3b5c97e3ce" />

I am running bootc 1.11.0