Fix broken url caused in docs (#17789)

### Description

Easy navigation and easy reading for others.

docs/advanced-features/codemods.md

@@ -132,7 +132,7 @@ export default withRouter(
 )
 ```
 
-This is just one case. All the cases that are transformed (and tested) can be found in the [`__testfixtures__` directory](./transforms/__testfixtures__/url-to-withrouter).
+This is just one case. All the cases that are transformed (and tested) can be found in the [`__testfixtures__` directory](https://github.com/vercel/next.js/tree/canary/packages/next-codemod/transforms/__testfixtures__/url-to-withrouter).
 
 #### Usage