[native] Remove unwrap in backup testing code

Summary: I left some unwraps() in the backup testing code instead of bubbling them up with ?. This code doesn't run without clicking a staff-only testing button, and will be removed soon anyway but this is just a quick fix so I made this diff.

Test Plan: N/A

Reviewers: bartek, kamil, varun

Reviewed By: bartek

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D10595