mrtest: allow installation of artifacts from partially finished ci runs

i don't know much about the gitlab api (or if this is even possible), but currently, an installation seems to be impossible if one of the jobs is in a failed/cancelled state, even if the one for the architecture you are on is complete. it would be nice if it was possible to install, say, x86_64 artifacts when the x86_64 build is complete, even if another arch failed/was cancelled (looking at it from the alpine side of things, but it seems to follow almost the same model here on pmaports)