Improve polymorphism in `typed_ast_test.ml`
Improve polymorphism in `typed_ast_test.ml`

Reviewed By: avikchaudhuri

Differential Revision: D12886207

fbshipit-source-id: e5e057ad58a8437b0a2bfb38ac9e5a40f04935d4

nmote/flow,nmote/flow,nmote/flow,nmote/flow,nmote/flow,nmote/flow,nmote/flow