Python 3.8 removed from latest ubuntu runners

[mjclarke94]

Python 3.8 is not present on the latest runner images for ubuntu, as it is no longer actively maintained. Not only does this result in a need to pin to older runner images, but means the deployment workflow relies on a version of python which doesn't receive security updates anymore.

Unpinning to just use whatever python version is present on the runner image might be the cleanest solution here.

[benpankow]

Thanks for the report, Matt - I believe to address this we'll need to publish a new dagster-cloud.pex on a more recent Python version - right now we only have published one for 3.8.

[ezpzbz]

@benpankow is there any tentative timeline when this is gonna happen? We still need to use ubuntu-20.04.
I just tried with action v0.1.43 and failed with the same reason
/usr/bin/env: ‘python3.8’: No such file or directory