Builds broken due to removal of Ubuntu 16.04 images from GitHub Actions

[probonopd]

Ouch! GitHub removed Ubuntu 16.04 from their default templates because it no longer receives standard support from Canonical:

• Remove Ubuntu 16.04 from templates actions/runner-images#4313
• Ubuntu 16.04 environment will be removed on September 20, 2021 actions/runner-images#3287
• Ubuntu 16.04 LTS Policy actions/runner-images#3082 (comment)

So we need to find another way to get it to run again. It's Docker after all, isn't it?

https://github.com/actions/virtual-environments says

We do not plan to offer other Linux distributions. We recommend using Docker if you'd like to build using other distributions with the hosted virtual environments.

Alternatively we could use 18.04 but it would be very unfortunate to artificially increase our system requirements for code that is known to build perfectly fine on 16.04.

Possibly(!) it would be wise to swtich to some open Source RHEL 7 clone to get improved long-term binary compatibility. Wdyt?

[TheAssassin]

16.04 has become obsolete/deprectated more than half a year ago and is now unmaintained. It is necessary to switch to the newer version, and nobody will care about anything else.

I do not intend to add any kind of Docker to the build infrastructure that is complex enough already. Using the oldest still-supported LTS is more than sufficient.

[probonopd]

actions/runner-images#4313 (comment)

@probonopd you can use container: option with ubuntu:16.04 as image https://docs.github.com/en/actions/learn-github-actions/workflow-syntax-for-github-actions#jobsjob_idcontainer

[TheAssassin]

Closed by #180.

[probonopd]

Does it still run on CentOS 7?