chore:update CONTRIBUTING.md style guide link (github#234)

Author: omihirofumi

CONTRIBUTING.md

@@ -2,7 +2,7 @@
 
 [fork]: https://github.com/github/github-mcp-server/fork
 [pr]: https://github.com/github/github-mcp-server/compare
-[style]: https://github.com/github/github-mcp-server/blob/main/.golangci.yaml
+[style]: https://github.com/github/github-mcp-server/blob/main/.golangci.yml
 
 Hi there! We're thrilled that you'd like to contribute to this project. Your help is essential for keeping it great.