Zip Slip in MarkUs config upload allowing RCE

MarkUs is a web application for the submission and grading of student assignments. Prior to 2.9.1, instructors are able to upload a zip file to create an assignment from an exported configuration (courses/<:course_id>/assignments/upload_config_files). The uploaded zip file entry names are used to create paths to write files to disk without checking these paths. This vulnerability is fixed in 2.9.1.