New remote-build fails with some architecture definitions

[mr-cal]

Bug Description

Snapcraft does not handle some definitions of architectures for remote builds and fails immediately with no error or explanation.

It's possible that other variations of architectures: will fail too, so we should add a set of regression tests.

To Reproduce

snapcraft remote-build

Environment

n/a

snapcraft.yaml

name: test-snap
version: '0.1'
summary: test
description: test

grade: devel
confinement: devmode

base: core22

architectures:
  - build-on: arm64


parts:
  my-part:
    plugin: nil

Relevant log output

All data sent to remote builders will be publicly available. Are you sure you want to continue? [y/N]: y
remote-build is experimental and is subject to change. Use with caution.
Build completed.
Log files:
Artifacts:

Additional context

From @jnsgruk on the snapcrafters channel (source)