tests: show that in-memory rebase leaves state when working copy is dirty

When in-memory rebase falls back to on-disk rebase, it checks if the
working copy is dirty. If it is, it aborts the rebase. However, it
leaves the rebase state on disk. I broke it in feffeb18d412 (rebase:
teach in-memory rebase to not restart with on-disk rebase on conflict,
2020-09-18).

Differential Revision: https://phab.mercurial-scm.org/D9508

tests/test-rebase-inmemory.t

@@ -487,6 +487,14 Retrying without in-memory merge won't l
   [255]
   $ cat a
   dirty
+  $ hg status -v
+  M a
+  # The repository is in an unfinished *rebase* state.
+  
+  # To continue:    hg rebase --continue
+  # To abort:       hg rebase --abort
+  # To stop:        hg rebase --stop
+  
 
 Retrying without in-memory merge won't lose merge state
   $ cd ..