When accepting a merge request, include VersionNum updates in binaries
At this point, GitLab launches a non-detached pipeline, but does so using the SHA from before srccommit did its thing to update the VersionNum (because this is performed using a hook at the git level that GitLab knows nothing about). The result is that the last artifacts presented on the MR page still have the version numbers at their pre-increment state. It's still possible to autobuild binaries with the new version number by manually launching a pipeline afterwards, but that's an extra step for a human to perform and so is undesirable. To attempt to deal with this, introduce a check on the environment variable CI_COMMIT_BRANCH. This is only set when the pipeline was launched based on a branch ref, and appears to include the case when an MR has just been merged. If so, we assume the "origin" remote contains a more up-to-date version of this branch ref (i.e. one with VersionNum updated) so we check that out before commencing the rest of the build steps. When launching a pipeline manually on a branch ref, this additional step should have no effect.