[GRASS-git] [OSGeo/grass] e4fd3a: CI: Do not run Docker job on forks (#1915)

[Vaclav Petras]

  Branch: refs/heads/main
  Home:   https://github.com/OSGeo/grass
  Commit: e4fd3aed299d1451cb12ec86c9895ea34b75c3cc
      https://github.com/OSGeo/grass/commit/e4fd3aed299d1451cb12ec86c9895ea34b75c3cc
  Author: Vaclav Petras <wenzeslaus at gmail.com>
  Date:   2021-10-03 (Sun, 03 Oct 2021)

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

  Log Message:
  -----------
  CI: Do not run Docker job on forks (#1915)

When a main branch is updated in fork, the workflow runs, but jobs fail because of missing credentials.
The workflow should not run in the first place. Currently, jobs need to be disabled individually.