[GRASS-git] [OSGeo/grass] e12718: GitHub action CI: drop ubuntu-16.04 (#1254)

[Markus Neteler]

  Branch: refs/heads/master
  Home:   https://github.com/OSGeo/grass
  Commit: e12718e7bf4f2597a59e31514d7c87aec982911b
      https://github.com/OSGeo/grass/commit/e12718e7bf4f2597a59e31514d7c87aec982911b
  Author: Markus Neteler <neteler at gmail.com>
  Date:   2021-01-16 (Sat, 16 Jan 2021)

  Changed paths:
    M .github/workflows/ci.yml

  Log Message:
  -----------
  GitHub action CI: drop ubuntu-16.04 (#1254)

Since ubuntu-16.04 is rather dated, drop it in GitHub action CI.