GHA deprecates ubuntu-16.04

[mdavidsaver]

Looks like GHA will be removing the ubuntu image we're using to test with older GCC.

actions/runner-images#3287

... we will remove Ubuntu 16.04 on September 20, 2021.

[mdavidsaver]

ppa:ubuntu-toolchain-r/test for ubuntu-18.04 (bionic) currently has GCC 9, 10, and 11.

[mdavidsaver]

Since our goal is really continued support for the likely long lived RHEL/Centos 7, maybe the goal should be to switch to some kind of container build. I've played with docker in this context. It works, but isn't so transparent. Perhaps some clever person has written an action which can conditionally execute via docker.

[ralphlange]

As I have mentioned in one of the last Telecons:
ci-scripts supports GitLab CI/CD, which runs all jobs in any Docker container that is available on Dockerhub.

[mdavidsaver]

I think the situation wrt. ubuntu-16.04 has now been addressed.