fix E251 in groups

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

about

```
E251 unexpected spaces around keyword / parameter equals
```

Component: **group theory**

Author: **Frédéric Chapoton**

Branch/Commit: **[`7dfb048`](https://github.com/sagemath/sagetrac-mirror/commit/7dfb0489c0c757e26e9a06af21f7799f518bde69)**

Reviewer: **David Coudert**

_Issue created by migration from https://trac.sagemath.org/ticket/34323_

