ci: define FDO_UPSTREAM_REPO
If this is not set, every fork will have to rebuild the image. This is not what we want for at least 2 reasons:
- forks are not running the CI in the same environment than the upstream project
- this infers bandwidth costs as every fork has its own image that needs to be pulled by every runner.
Note that this will also make the docker build stage faster for forks as they won't have to rebuild anything.
Fixes !372 (merged)
Signed-off-by: Benjamin Tissoires benjamin.tissoires@gmail.com