package-repositories assumes architecture

snapcraft: 7.1.3
base: core20

snapcraft.yaml:

package-repositories:
    - type: apt
      ppa: snappy-dev/image

This results in:
snapcraft-ppa-snappy-dev_image.sources with the following content:
Types: deb
URIs: http://ppa.launchpad.net/snappy-dev/image/ubuntu
Suites: focal
Components: main
Architectures: arm64

If "architectures" was not specified in "package-repositories", snapcraft should not assume it, and omit "Architectures" in the generated source file.