minor: visit_Assert: move setting of `negation` out of branches
minor: visit_Assert: move setting of `negation` out of branches

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