docs: advanced: Fix Keyring move example script
docs: advanced: Fix Keyring move example script

The given script moves the keyring files on the currently active slot
instead of the target slot.

Signed-off-by: Christoph Steiger <3f91aa653aebbbdccba05966de7ea332718b6802@lemonage.de>

rauc/rauc,jluebbe/rauc,ejoerns/rauc,rauc/rauc,jluebbe/rauc,ejoerns/rauc,jluebbe/rauc,rauc/rauc,ejoerns/rauc