Allow flashing to inactive slot

[viridivn]

Seems like currently you can only flash the active slot. It would be nice for updates to be able to flash the inactive slot

[kappa-maintainer]

https://github.com/YuKongA/KernelFlasher/actions/runs/7245341156

[viridivn]

Thanks! I had to rebuild it myself because the CI was unsigned but it seems to work well. Backing up inactive slot is also very handy. Has @YuKongA considered making a PR to this repo with the modified code?

[capntrips]

This topic was also discussed in #11, I figured I would note that here.