make sure the framework tests run with the proper environment
only when when there is something to undo

They hypothesis behind this change is that the undo is
undoing an edit that came before, not the temporary edit
that appears in insert-close-paren. So, when there are
no edits happening (ie when fixup? is #f) then don't
undo. This is only a hypothesis because we were not able
to find a small code sequence, outside of DrRacket to
cause the bad behavior, so possibly there is really more
going on here.

Thanks to Nadeem Abdul Hamid for finding this fix.

Closes PR 13454