hg-git: added base images for tests with Python 3
we'll have one for an unspecified Mercurial version, to be updated to default or stable within the build, and one on Mercurial 5.3
This instance will be upgraded to Heptapod 17.2.2 on 2024-09-12 at 17:00 UTC+2
we'll have one for an unspecified Mercurial version, to be updated to default or stable within the build, and one on Mercurial 5.3