### Bug Description Building a charm on a non-amd64 architecture using the legacy Charmcraft 2 `bases` notation on Charmcraft 3 ignores the architecture and defaults to amd64 despite building on a different platform. Example for this is the [postgresql-tes-app](https://github.com/canonical/postgresql-test-app) packing and CI tests passed fine, using a locally packed charm, but both amd64 and arm64 revisions got published as amd64 revisions. The `manifest.yaml` inside the published arm64 revison (203) is: ``` charmcraft-version: 3.1.1 charmcraft-started-at: '2024-08-02T10:30:16.196847' bases: - name: ubuntu channel: '22.04' architectures: - amd64 - name: ubuntu channel: '22.04' architectures: - arm64 analysis: attributes: - name: language result: python - name: framework result: operator ``` The packed charm is correctly marked as arm64 ### To Reproduce * Pack postgresql-test-app on arm64 * Publish on charmhub * Deploy on amd64 ### Environment OS: Ubuntu 22.04 (Github runner) Charmcraft: 3.1.1 ### charmcraft.yaml ```shell # Copyright 2023 Canonical Ltd. # See LICENSE file for licensing details. type: charm bases: - name: ubuntu channel: "22.04" architectures: [amd64] - name: ubuntu channel: "22.04" architectures: [arm64] parts: charm: override-pull: | craftctl default if [[ ! -f requirements.txt ]] then echo 'ERROR: Use "tox run -e build" instead of calling "charmcraft pack" directly' >&2 exit 1 fi charm-strict-dependencies: true libpq: build-packages: - libpq-dev plugin: dump source: /usr/lib/ source-type: local prime: - lib/ organize: "*-linux-gnu/libpq.so*": lib/ ``` ### Relevant log output ```shell Packing... Packing charm postgresql-test-app_ubuntu-22.04-arm64.charm Packed postgresql-test-app_ubuntu-22.04-arm64.charm build-dev: commands_post[0]> mv requirements.txt requirements-last-build.txt build-dev: OK (304.68=setup[0.95]+cmd[0.66,303.07,0.00] seconds) congratulations :) (304.74 seconds) ```