Remove ubuntu-20.04 from CI test matrix, since Github is removing support

[jafingerhut]

See p4lang/p4c#5155 for more background.

[vgurevich]

Do you build the Linux kernel modules during testing? I've seen them failing to build on Ubuntu 22.04

[jafingerhut]

Do you build the Linux kernel modules during testing? I've seen them failing to build on Ubuntu 22.04

I do not know what in the profiles YAML file controls that. Please create a PR modifying the testing.yaml file, and the CI test results should eventually show whether it builds successfully or not on the Ubuntu 22.04 CI system.

Given the change Github is making on April 1, we need to make a change like the one in this PR by then, regardless of whether kernel modules build on Ubuntu 22.04 or not.

If someone wants to continue testing open-p4studio builds on Ubuntu 20.04 after April 1, they will need to create Github actions that use a Docker container with Ubuntu 20.04 as the guest OS, or something similarly effective. I have no plans to do so.

[fruffy]

Isn't the implication that we will also drop support for Ubuntu 20.04 in general? There is a lot of code and several workarounds dedicated to it. It will be hard to make guarantees without CI testing long-term.

[jafingerhut]

Isn't the implication that we will also drop support for Ubuntu 20.04 in general? There is a lot of code and several workarounds dedicated to it. It will be hard to make guarantees without CI testing long-term.

It might be worth creating a tag of this repo with the last version on which it was built and tested on Ubuntu 20.04, for people wanting to go back to that version.

[vgurevich]

I think that before we stop supporting Ubuntu-20.04, we need to ensure we can support Ubuntu-22.04, should we not? And I am afraid that currently this is not fully the case. Moreover, this might require significant testing effort upfront, way more than an individual like myself is able to contribute.

[jafingerhut]

I think that before we stop supporting Ubuntu-20.04, we need to ensure we can support Ubuntu-22.04, should we not? And I am afraid that currently this is not fully the case. Moreover, this might require significant testing effort upfront, way more than an individual like myself is able to contribute.

Sorry to repeat myself, but the changes in this PR are necessary in order to avoid CI tests on this repo failing completely every time as of April 1.

Whether or not we continue supporting Ubuntu 20.04 in terms of restrictions on the kinds of code changes made, or in CI, can be done separately from this PR.