Run stack test workflows on ubuntu 24.04

[robdimsdale]

• The version of skopeo that runs on ubunut 22.04 is too old for the version of docker now installed on github action runners.
• it is very hard to update skopeo on the runners - they just install whatever is available upstream by ubuntu (and skopeo does not publish pre-built binaries)
• our options are either compile from source every time we need skopeo (ineffient and brittle), manually install skopeo from a third-party ppk (also somewhat slow and sketchy) or use a runner with a newer version of ubuntu and hence skopeo (fastest, least brittle).
• we update every instance of a runner in the workflows that use skopeo against the local daemon to avoid any potential issues that might occur when hopping between runner versions during workflow execution.