multi-arch-test-build: run it only after the Formality check succeeds

multi-arch-test-build: run it only after the Formality check succeeds

Most of the time, when people contribute to the repository for the first time
 (or after a longer break), the multi-arch-test-build passes, but the
formality check fails and requires the contributor to make some changes.

This creates unnecessary load on the CI/CD, since the multi-arch-test-build
runs again even though it already passed, while other PRs are waiting for a runner.
Hopefully, this change will help decrease the waiting time.

Proposed changes:

- Run the formality check first, and only trigger the package tests afterwards.
This can be done using needs: https://docs.github.com/en/actions/reference/workflows-and-actions/workflow-syntax#jobsjob_idneeds

- Merge formal.yml into multi-arch-test-build.yml so that needs can be used.

Signed-off-by: Josef Schlehofer <[email protected]>