Tasks aren't actually lightweight :frown:

Fixes #19402.
My thought process was basically 'tasks are threads but our type system prevents some stuff that makes them safer than threads in other languages, and if they are threads, that calls into question why they aren't just called threads, and they're going to be at some point, but then we are gonna revise all this anyway, soooooo whatever.'

I wouldn't mind if it just said that though.=