docs(index): fix dead pydantic-extra-types link

docs.pydantic.dev/latest/usage/types/extra_types/extra_types/ returns 404
(pydantic v1 /usage/types/ retired). Replace with the v2 canonical
/docs/latest/concepts/types/#extra-types (200). Same fix as #15822 which
covered release-notes.md.

docs/en/docs/index.md

@@ -573,7 +573,7 @@ There are some additional dependencies you might want to install.
 Additional optional Pydantic dependencies:
 
 * [`pydantic-settings`](https://docs.pydantic.dev/latest/usage/pydantic_settings/) - for settings management.
-* [`pydantic-extra-types`](https://docs.pydantic.dev/latest/usage/types/extra_types/extra_types/) - for extra types to be used with Pydantic.
+* [`pydantic-extra-types`](https://docs.pydantic.dev/latest/concepts/types/#extra-types) - for extra types to be used with Pydantic.
 
 Additional optional FastAPI dependencies: