Jump to upstream GitLab Runner 13.3
This rebases Heptapod Runner on top of GitLab Runner 13.3.1 and brings along various test improvements.
At this point, make tests
succeeds in my development setup (Ubuntu 20.04, with VirtualBox/Vagrant and Docker, but without Parallels and Kubernetes. In particular, all tests for the Docker executor pass.
There are simplifications to be made in the build, probably to get closer to upstream. It should improve the cross-compilation capabilities.
Overall this is a much nicer base for further version jumps and portability.