ci: Explicitly use Ubuntu 24.04 for our runner images

[apyrgio]

GitHub actions somehow managed to downgrade our runners from Ubuntu 24.04 to Ubuntu 22.04, even though we use ubuntu-latest. Make the Ubuntu 24.04 requirement more explicit, until GitHub migrates fully to this version for the ubuntu-latest tag.

Fixes #957

[almet]

The problem seem to already have been reported upstream (actions/runner-images#10796 and actions/runner-images#10767).

On the short term, I think we should merge your fix, but I also think that using ubuntu-latest makes more sense in the long term, once the problem is fixed on the github CI.

[almet]

You can actually follow the actual discussion here: actions/runner-images#10636

[almet]

but I also think that using ubuntu-latest makes more sense in the long term, once the problem is fixed on the github CI.

... Reading the thread actually made me change my mind: we'll be better off with using a specific tag and upgrading it when a new release is out.

As part of checking new releases and adding support for them, we could also bump the image used by our runners to reflect this.