tests: demonstrate how continuing rebase after upgrade can result in merge If the user starts a rebase with an hg version before 9c9cfecd4600 (rebase: don't use rebased node as dirstate p2 (BC), 2020-01-10) and then runs into conflicts, they will be dropped out to the shell with the rebased node set as the dirstate's second parent. If they then upgrade to a later hg version, it will respect the dirstate's parents and will create a merge commit even if the user was rebasing a non-merge commit. Differential Revision: https://phab.mercurial-scm.org/D8355