RAID ESP breaks firmware updater

[IohannesArnold]

• Model: darp9
• BIOS version: 2023-08-18_a8dd6c2
• EC version: 2023-08-18_a8dd6c2
• OS: Pop!_OS 22.04 LTS
• Kernel: 6.8.0-76060800daily20240311-generic

If the EFI System Partition is configured as RAID-1 (yes it is possible), the System76 Firmware updater does not work (neither GUI nor CLI).

Steps to reproduce

1. Create an mdadm RAID 1 array with metadata format 1.0 to serve as ESP.
2. Attempt to update firmware.

Expected behavior

1. The firmware updates.

Actual behavior

1. The updater fails with the error: error in system76-firmware client: calling Schedule method failed: failed to read /sys/devices/virtual/block/md126/partition: No such file or directory (os error 2)

Additional info

I realize this is a fairly unusual configuration, and I won't be shocked if this turns out to be a #wontfix. But a bit more documentation about how to manually stage files for a firmware update would be helpful at least.