main/postmarketos-release-upgrade: upgrade to 1.2.1

Has an important fix for samsung-a5 and other samsung devices where udev rules were moved to postmarketos-base. Currently the upgrade reports an error there when it's done and the user has to manually run apk fix and reboot afterwards. (https://gitlab.com/postmarketOS/postmarketos-release-upgrade/-/issues/4)

Quite important, merging after CI passes.