tweak badge design

Author: dbu

README.md

@@ -2,7 +2,7 @@
 
 [![Latest Version](https://img.shields.io/github/release/php-http/message.svg?style=flat-square)](https://github.com/php-http/message/releases)
 [![Software License](https://img.shields.io/badge/license-MIT-brightgreen.svg?style=flat-square)](LICENSE)
-[![tests](https://img.shields.io/github/actions/workflow/status/php-http/message/tests.yml?branch=1.x&label=tests)](https://github.com/php-http/message/actions/workflows/ci.yml)
+[![tests](https://img.shields.io/github/actions/workflow/status/php-http/message/tests.yml?branch=1.x&label=tests&style=flat-square)](https://github.com/php-http/message/actions/workflows/tests.yml)
 [![Total Downloads](https://img.shields.io/packagist/dt/php-http/message.svg?style=flat-square)](https://packagist.org/packages/php-http/message)
 
 **HTTP Message related tools.**