Unbreak //exectorch/docs:doctest internally (#8693)

Added missing buck dep.

Differential Revision: [D70099706](https://our.internmc.facebook.com/intern/diff/D70099706/)

ghstack-source-id: 268011090
Pull Request resolved: https://github.com/pytorch/executorch/pull/8645

Co-authored-by: Scott Wolchok <swolchok@meta.com>