ci: Trigger the docker image build on merge requests
Our current CI setup doesn't specify a proper dependency between the build and test CI stages for merge requests, since the test stage jobs are triggered on 'merge_requests' whereas the build stage jobs are not.
This leads to both build and test jobs starting in parallel for merge requests, potentially leading to the tests running with an older docker image.
This patch triggers the build stage jobs on 'merge_requests' ensuring correct dependencies.
Signed-off-by: Alexandros Frantzis alexandros.frantzis@collabora.com