Replace flatten() with chain.from_iterable
Replace flatten() with chain.from_iterable

flatten is an alias in more-itertools anyway

The-Compiler/pytest,markshao/pytest,Akasurde/pytest,nicoddemus/pytest,alfredodeza/pytest,nicoddemus/pytest,RonnyPfannschmidt/pytest,tomviner/pytest,tomviner/pytest,pytest-dev/pytest,The-Compiler/pytest