sage.manifolds, sage.tensor: Fix spelling errors

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

Fix spelling errors in `sage.manifolds, sage.tensor`.

CC:  @egourgoulhon

Component: **manifolds**

Author: **Matthias Koeppe**

Branch/Commit: **[`2fc6089`](https://github.com/sagemath/sagetrac-mirror/commit/2fc6089e119d29653cd8a3e487428add8afcf1a6)**

Reviewer: **Kwankyu Lee**

_Issue created by migration from https://trac.sagemath.org/ticket/33539_

