Weekly alpha build are a bit annoying because:

• they fail often due to use using [patch] on egui & co
• they only build crates, not the other artefacts
• they are implemented using a different workflow than releases, leading to confusion and duplication

They were initially implemented for:

• making sure that the crate upload process isn't broken
• artefact are available for use by adventurous users

However:

• the nightly builds produce "dev" artefacts that are usable
• alphas are really easy to trigger manually if needed
• the release workflow (with rc &co) now is much better at catching any publication breakage before the actual release

So.... let's remove weekly alpha builds