Allow running security MR pipelines during validation
When using pipelines for merged results, we create a new pipeline prior to merging, which due to the duration of the pipeline, would cause the next validation run to kick the MR back to the author, even though we had approved it and started its merging process.
This change allows a running pipeline for a merge request targeting
master, since if it fails it will be properly reassigned during the
next validation run.
Merge requests not targeting master are still reassigned because we
don't create the pipeline for merge result there.