- remove `builder_is_running_on_ci` function since there already is a
similar `builder_is_ci_build` function
- use `GITHUB_ACTIONS` environment variable instead of `GITHUB_RUN_ID`
to detect if we're run be GitHub Actions
This adds the three additional functions `builder_is_running_on_ci`,
`builder_is_running_on_docker`, and `builder_is_running_on_gha` to be
able to detect if the build is running in a CI or CI-like container
environment.
