Update README.md

Author: Takeshi Yu

README.md

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 A Composer plugin for linking local packages during development, similar to `npm link`.
 
 <p align="center">
-    <a href="https://github.com/takeshiyu/composer-linker/actions"><img src="https://github.com/takeshiyu/composer-linker/workflows/tests/badge.svg" alt="Build Status"></a>
+    <a href="https://github.com/username/composer-linker/actions/workflows/php.yml"><img src="https://github.com/takeshiyu/composer-linker/actions/workflows/php.yml/badge.svg" alt="Build Status"></a>
 </p>
 
 ## Key Features