chore: use upload-artefact@v7 archive=false feature

[dimaqq]

Direct Uploads
Adds support for uploading single files directly (unzipped). Callers can set the new archive parameter to false to skip zipping the file during upload. Right now, we only support single files.

https://github.com/actions/upload-artifact/releases/tag/v7.0.0

we'd then adjust the steps that use download-artefact too.

[benhoyt]

@dimaqq Can you please elaborate on what advantage this would bring, that is, not to zip up the files during the upload-artifact step?

[dimaqq]

Today, we're uploading and downloading an archive only because that's what the tooling and github API allowed.
IMO, it's a bit of a wart, I had to sort it out by trial and error in #736 #742 #746 which took a calendar week to get sorted.
While GitHub 1st party actions are generally pretty stable, I'm still a little worried that one day the new archive= flag default value may eventually get toggled, see actions/upload-artifact#764

We may decide not to after looking into the issue deeper, that's fine.

Caveat developer: this action is used for two distinct purposes

• uploading build logs -- out of scope
• moving the built snap between the build step and publish