fix docker workflow by running on push to main, rather than master

[emiltin]

No description provided.

[emiltin]

It means packages on https://github.com/orgs/rsmp-nordic/packages?repo_name=rsmp_validator was not updated. Should be fixed, but can't verify until this PR is merged to main :-)

[emiltin]

There are a number of build warnings, see: https://github.com/rsmp-nordic/rsmp_validator/actions/runs/7553773064
@otterdahl do you want to have a look at fixing those?

[emiltin]

The packages is now being build: https://github.com/rsmp-nordic/rsmp_validator/pkgs/container/rsmp_validator.

[otterdahl]

There are a number of build warnings, see: https://github.com/rsmp-nordic/rsmp_validator/actions/runs/7553773064 @otterdahl do you want to have a look at fixing those?

I believe that build-push-action needs to updated. I've created a PR #370, but I can't verify because the github action won't run until merged to main. I'll merge anyway and we'll see.

[otterdahl]

Seems to be fixed