[MusicXML import] [1.2] import error: 41d-StaffGroups-Nested.xml: part-group symbol=line not supported

File 41d-StaffGroups-Nested.xml in Reinhold Kainhofers unofficial MusicMXL testsuite does not import the part-group with symbol=line. Although his type is not supported by MuseScore, it would be better to import the part-group as a supported type.