docs: reference for server.moduleGraph in per-environments-apis migrations (vitejs#20185)

Author: mrcego

docs/changes/per-environment-apis.md

@@ -28,6 +28,6 @@ In Vite v6, it is now possible to create any number of custom environments (`cli
 
 ## Migration Guide
 
-- `server.moduleGraph` -> [`environment.moduleGraph`](/guide/api-environment#separate-module-graphs)
+- `server.moduleGraph` -> [`environment.moduleGraph`](/guide/api-environment-instances#separate-module-graphs)
 - `server.transformRequest(url, ssr)` -> `environment.transformRequest(url)`
 - `server.warmupRequest(url, ssr)` -> `environment.warmupRequest(url)`