CI select OS version

Many CI services use Ubuntu Linux images. The default Linux / Ubuntu version is typically an older version. It can be convenient to switch CI jobs to a newer Linux version to get more recent libraries. Here are examples of switching Linux version for a few popular CI services.

GitHub Actions default Ubuntu version is controlled with .github/workflows/*.yml file(s). For example, Ubuntu 20.04 may be selected with

jobs:

  linux:
    runs-on: ubuntu-20.04