docs(changelog): re-target MsgspecDTO/PydanticDTO refs to current locations

The 2.x changelog entry for the original DTO factories had its two
`:class:` cross-refs demoted to literal backticks during the contrib
namespace cleanup, but the symbols still exist — they just moved.
Re-point them at the canonical Sphinx targets (`litestar.dto.msgspec_dto.MsgspecDTO`
and `litestar.plugins.pydantic.PydanticDTO`) so the historical bullets
link to live API pages again. `make docs` builds warning-free.

Author: cofin

docs/release-notes/2.x-changelog.rst

@@ -2703,8 +2703,8 @@
         DTO factories for `msgspec <https://jcristharif.com/msgspec/>`_ and
         `Pydantic <https://docs.pydantic.dev/latest/>`_ have been added:
 
-        - ``MsgspecDTO``
-        - ``PydanticDTO``
+        - :class:`~litestar.dto.msgspec_dto.MsgspecDTO`
+        - :class:`~litestar.plugins.pydantic.PydanticDTO`
 
     .. change:: DTOs: Arbitrary generic wrappers
         :pr: 1801