In MRI, `Thread#[]`/`Thread#[]=` and `Thread#thread_variable_get`/`thread_variable_set` differ in an important way once fibers are involved. What does this program print?
Thread.current[:k] = "outer"
Thread.current.thread_variable_set(:k, "outer-tv")
Fiber.new do
p Thread.current[:k]
p Thread.current.thread_variable_get(:k)
end.resume