Pylint dunder calls

https://gitup.uni-potsdam.de/innohs/rest-api/-/jobs/95861

************* Module articles.views
articles/views.py:107:7: C2801: Unnecessarily calls dunder method __contains__. Use in keyword. (unnecessary-dunder-call)
articles/views.py:492:11: C2801: Unnecessarily calls dunder method __contains__. Use in keyword. (unnecessary-dunder-call)
articles/views.py:493:15: C2801: Unnecessarily calls dunder method __contains__. Use in keyword. (unnecessary-dunder-call)
************* Module prediction.train_data
prediction/train_data.py:174:31: R1736: Unnecessary list index lookup, use '_' instead (unnecessary-list-index-lookup)
prediction/train_data.py:178:30: R1736: Unnecessary list index lookup, use '_' instead (unnecessary-list-index-lookup)
prediction/train_data.py:238:31: R1736: Unnecessary list index lookup, use '_' instead (unnecessary-list-index-lookup)