heptapod-shell: using evolve/topic to fetch source repo

It helps with the botched case of heptapod-13.19.2 tag, that was
later on fixed with an obsolescence marker (change of branch IIRC)

--HG--
branch : heptapod-stable
4 jobs for !52 with topic/heptapod-stable/bump-stable in 84 minutes and 34 seconds (queued for 3 seconds)
latest merge request