Remove unsafe returned value from swap

Author: morgen-peschke

docs/std/nonemptyhotswap.md

@@ -16,7 +16,7 @@ to `Hotswap` which remove the `Option` wrapper.
 
 ```scala
 sealed trait NonEmptyHotswap[F[_], R] {
-  def swap(next: Resource[F, R]): F[R]
+  def swap(next: Resource[F, R]): F[Unit]
   def get: Resource[F, R]
 }
 ```

std/shared/src/main/scala/cats/effect/std/NonEmptyHotswap.scala

@@ -117,12 +117,12 @@ object NonEmptyHotswap {
       Resource.make(initialize)(finalize).map { state =>
         new NonEmptyHotswap[F, R] {
 
-          override def swap(next: Resource[F, R]): F[R] =
+          override def swap(next: Resource[F, R]): F[Unit] =
             F.uncancelable { poll =>
               poll(next.allocated).flatMap {
                 case (r, fin) =>
                   exclusive.mapK(poll).onCancel(Resource.eval(fin)).surround {
-                    swapFinalizer(Acquired(r, fin)).as(r)
+                    swapFinalizer(Acquired(r, fin))
                   }
               }
             }