drm_hwcomposer: CI: Only run build-docker when necessary
When building the docker image via docker in docker, we sometimes see system errors such as:
*** WARNING: Service runner-zcexkv2-project-23176-concurrent-0-14607a9f5e2c806b-docker-0 probably didn't start properly.
Health check error:
create service container: Error response from daemon: bad parameter: link is not supported (services.go:208:0s)
Service container logs:
*********
This hinders all merge requests.
Limit the build-docker job to be only ran when .ci/Dockerfile is modified.
Link: #96 (closed) Signed-off-by: Mattijs Korpershoek mkorpershoek@baylibre.com