Ensure we unwrap custom .then()

[JoviDeCroock]

Fixes #3219

Before this fix we would return { default: JSX.Element } which is obviously wrong 😅

[rschristian]

Neat type and TIL! Somehow I've never ran across infer before

[coveralls]

coverage: 99.488%. remained the same
when pulling cbeb27f on fix-lazy-types
into aee8285 on main.