Add tests badge

Author: Holger Lösken

README.md

@@ -2,6 +2,7 @@
 
 ![Statamic 3.0+](https://img.shields.io/badge/Statamic-3.0+-FF269E?style=for-the-badge&link=https://statamic.com)
 [![Latest Version on Packagist](https://img.shields.io/packagist/v/codedge/statamic-magiclink?style=for-the-badge)](https://packagist.org/packages/codedge/statamic-magiclink)
+![Tests](https://github.com/codedge/statamic-magiclink/workflows/Tests/badge.svg)
 
 A Statamic V3 addon to provide the option to login into the Control Panel without using a password. Instead use a magic link
 which is sent by email.