Fix coverage badge in README.md

This was mangled by 8507cef due to a
copypaste bug.

Author: ednolan

README.md

@@ -6,7 +6,7 @@ SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 ![Continuous Integration Tests](https://github.com/bemanproject/task/actions/workflows/ci_tests.yml/badge.svg)
 ![Target Standard](https://github.com/bemanproject/beman/blob/main/images/badges/cpp26.svg)
-![Coverage](https://coveralls.io/repos/github/bemanproject/task/badge.svg?branch=main)](https://coveralls.io/github/bemanproject/task?branch=main)
+![Coverage](https://coveralls.io/repos/github/bemanproject/task/badge.svg?branch=main)
 
 `beman::execution::task<T, Context>` is a class template which
 is used as the the type of coroutine tasks. The corresponding objects