Fix Tests badge (#17)

The workflow name is case-sensitive, and `tests` is an earlier workflow we no
longer use.

Author: cjolowicz

README.md

@@ -1,4 +1,4 @@
-[![tests](https://github.com/cjolowicz/hypermodern-python/workflows/tests/badge.svg)](https://github.com/cjolowicz/hypermodern-python/actions?workflow=tests)
+[![Tests](https://github.com/cjolowicz/hypermodern-python/workflows/Tests/badge.svg)](https://github.com/cjolowicz/hypermodern-python/actions?workflow=Tests)
 [![Codecov](https://codecov.io/gh/cjolowicz/hypermodern-python/branch/master/graph/badge.svg)](https://codecov.io/gh/cjolowicz/hypermodern-python)
 [![PyPI](https://img.shields.io/pypi/v/hypermodern-python.svg)](https://pypi.org/project/hypermodern-python/)
 [![Read the Docs](https://readthedocs.org/projects/hypermodern-python/badge/)](https://hypermodern-python.readthedocs.io/)