remove best effort support for ubuntu 18.04

[dmah42]

as of 2022-01-12, github removed support for ubuntu-18.04. as such, we are removing it from github actions and no longer will support it actively.

it was already "best effort" but time marches on.

[LebedevRI]

While i don't have an opinion on what we should do regarding supporting that particular distro,
i feel like i should point out that it is not relevant what linux distributions are natively supported
by github runners, because there's such thing as a docker, with idea being:
use the freshest distro in runs-on: field, and then just pick the distro you want
(from whatever the source, e.g. https://hub.docker.com/_/ubuntu), and specify it in container: image:
That is what i have always been doing, at least.

See https://docs.github.com/en/actions/using-jobs/running-jobs-in-a-container

[dmah42]

While i don't have an opinion on what we should do regarding supporting that particular distro, i feel like i should point out that it is not relevant what linux distributions are natively supported by github runners, because there's such thing as a docker, with idea being: use the freshest distro in runs-on: field, and then just pick the distro you want (from whatever the source, e.g. https://hub.docker.com/_/ubuntu), and specify it in container: image: That is what i have always been doing, at least.

See https://docs.github.com/en/actions/using-jobs/running-jobs-in-a-container

yeah, we could. i'm ok with dropping support for this particular platform though.

[dmah42]

maybe we can use containers for the sanitizer builds... or at least a shared cache so we don't keep rebuilding the world for each one.

[dmah42]

sanitizer builds are timing out.. that's next on my list.