Merging the Error Channel into the Success Channel

With ZIO#merge we can merge the error channel into the success channel:

import zio._

val merged : ZIO[Any, Nothing, String] =
  ZIO.fail("Oh uh!") // ZIO[Any, String, Nothing]
    .merge           // ZIO[Any, Nothing, String]

If the error and success channels were of different types, it would choose the supertype of both.