tests: try to fix ubuntu bionic tests

[lazka]

by forcing an older nodejs

the node v20 build no longer works in bionic. While actions/checkout@v3 uses node v16 GHA forced it to use v20 some time ago after a deprecation cycle. This env var makes it use v16 again, despite that being EOL.

[jpakkane]

Bionic has been EOL since 2023-05-31. I'd say let's move that container to Focal instead.

[eli-schwartz]

Bionic currently tests that we maintain support for Python 3.7 (and I don't want to bump the minimum version of python until we are using features that require the new version -- we still occasionally get complaints that meson dropped 3.6 support but I spearheaded that upgrade because of tangible developer advantages in moving to 3.7, not just "GitHub broke the CI so we don't test it").

Beyond that, I saw at least one claim that the GitHub Actions nodejs issue affects Ubuntu 20.04 (focal) containers as well, but I haven't verified.

[lazka]

Fine with me either way. This makes the CI green though in the meantime.

[lazka]

A middle ground could be Debian Buster, Python 3.7, newer glibc, EOL since two weeks.

[dcbaker]

In the interest of having a green CI, I'm going to merge this. If we want to move to Focal or Buster we can do that as a separate PR

[lazka]

thanks!