tests: adjust deflists test for PyMD 2.1
tests: adjust deflists test for PyMD 2.1

Since PyMD 2.1, multi-line descriptions in defintion lists do not need
to be indented, i.e. unindented continuation lines do not break
definition lists anymoe. This also means that multi-line descriptions
must be followed by a new line.

obensonne/markowik