Update config-shared docs link (vercel#44547)

Closes: vercel#44542

## Documentation / Examples

- [x] Make sure the linting passes by running `pnpm build && pnpm lint`
- [x] The "examples guidelines" are followed from [our contributing
doc](https://github.com/vercel/next.js/blob/canary/contributing/examples/adding-examples.md)

docs/api-reference/next.config.js/introduction.md

@@ -80,7 +80,7 @@ module.exports = (phase, { defaultConfig }) => {
 }
 ```
 
-The commented lines are the place where you can put the configs allowed by `next.config.js`, which are [defined in this file](https://github.com/vercel/next.js/blob/canary/packages/next/server/config-shared.ts#L158).
+The commented lines are the place where you can put the configs allowed by `next.config.js`, which are [defined in this file](https://github.com/vercel/next.js/blob/canary/packages/next/src/server/config-shared.ts).
 
 However, none of the configs are required, and it's not necessary to understand what each config does. Instead, search for the features you need to enable or modify in this section and they will show you what to do.