System partition is not an EFI System Partition

Originally created by @intrigeri on #16153 (Redmine)

I’ve started a Tails USB stick installed with a USB image built from the topic branch and GNOME Disks tells me the system partition type is “Basic Data”. It should be an ESP, otherwise at least some EFI systems won’t boot from it. I don’t know if that’s a regression introduced by bbbe90de or if sgdisk --randomize-guids is about another GUID than this one.

This may block writing automated tests for booting from EFI (not tested yet though), hence the higher than normal priority.

Feature Branch: feature/15292-generate-usb-image

Parent Task: #15293 (closed)