Fix test_setup_loop_dev on CI

[mxpv]

Looks like one of the tests is failing:

failures:

---- mount_linux::tests::test_setup_loop_dev stdout ----
thread 'mount_linux::tests::test_setup_loop_dev' panicked at crates/shim/src/mount_linux.rs:1174:9:
assertion failed: result.is_ok()
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace


failures:
    mount_linux::tests::test_setup_loop_dev

[mxpv]

@zzzzzzzzzy9 can you take a look pls?

[zzzzzzzzzy9]

That's ok, I will take a look.