GitHub Actions: raise upload-artifact + download-artifact to v4

[mika]

Fixes:

| Node.js 16 actions are deprecated. Please update the following actions to use Node.js 20: actions/download-artifact@v3, actions/upload-artifact@v3.
| For more information see: https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/.

Related to #278

Thanks: Darshaka Pathirana

[evgeni]

Is the matrix release somewhere part of the .deb name? V4 fails if you try to upload the same filename twice

[evgeni]

Ah, just realized the release name is part of the artifact bame

[mika]

Is the matrix release somewhere part of the .deb name? V4 fails if you try to upload the same filename twice

Uh thanks for the pointer! We have:

     - name: Archive built .deb
      uses: actions/upload-artifact@v4
       with:
         name: deb-${{matrix.host_release}}
[...]
     - name: Download built deb
      uses: actions/download-artifact@v4
       with:
         name: deb-${{matrix.host_release}}
[...]
     - name: Archive VM test results
      uses: actions/upload-artifact@v4
       with:
         name: vm-results-${{matrix.host_release}}-${{matrix.release}}-${{matrix.debootstrap}}

I suppose this should be "safe" then?

[zeha]

ok once the ci jobs (that are known to pass) pass