Add comma in vscode.json config file

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

There is a missing comma in `.vscode/setting.json`. 

Component: **misc**

Keywords: **vscode**

Author: **David Ayotte**

Branch/Commit: **[`3a58015`](https://github.com/sagemath/sagetrac-mirror/commit/3a58015943a8b7497e0cf1143c3dc6e51de03867)**

Reviewer: **Matthias Koeppe**

_Issue created by migration from https://trac.sagemath.org/ticket/34352_

