In CI, determine loop devices dynamically to avoid conflicts with Ubuntu snaps
In CI, determine loop devices dynamically to avoid conflicts with Ubuntu snaps

Introduced when updating CI to Ubuntu 20.04, Ubuntu snaps consume
loop devices, which conflict with out assumption that /dev/loop0
will always be unused. Changed to request a dynamic loop device from
losetup, though it would have been nice if Ubuntu snaps allocated
from the last device or something.

littlefs-project/littlefs,littlefs-project/littlefs