fix E502 in some pyx files

<div id="comment:0"></div>

mostly inside matrix/

Component: **refactoring**

Author: **Frédéric Chapoton**

Branch/Commit: **[`04ac04c`](https://github.com/sagemath/sagetrac-mirror/commit/04ac04c2f0cb16a5d3b7ca8403a46529ddaa24ca)**

Reviewer: **Matthias Koeppe**

_Issue created by migration from https://trac.sagemath.org/ticket/34837_

