maintain: fix GitHub Actions badge

Author: hukkin

README.md

@@ -1,7 +1,7 @@
 <div align="center">
 
 [![Documentation Status](https://readthedocs.org/projects/mdformat/badge/?version=latest)](https://mdformat.readthedocs.io/en/latest/?badge=latest)
-[![Build Status](https://github.com/hukkin/mdformat/workflows/Tests/badge.svg?branch=master)](https://github.com/hukkin/mdformat/actions?query=workflow%3ATests+branch%3Amaster+event%3Apush)
+[![Build Status](https://github.com/hukkin/mdformat/actions/workflows/tests.yaml/badge.svg?branch=master)](https://github.com/hukkin/mdformat/actions?query=workflow%3ATests+branch%3Amaster+event%3Apush)
 [![codecov.io](https://codecov.io/gh/hukkin/mdformat/branch/master/graph/badge.svg)](https://codecov.io/gh/hukkin/mdformat)
 [![PyPI version](https://img.shields.io/pypi/v/mdformat)](https://pypi.org/project/mdformat)