Make joinWithNever attempting self cancelling

kernel/shared/src/main/scala/cats/effect/kernel/Fiber.scala

@@ -68,10 +68,11 @@ trait Fiber[F[_], E, A] extends Serializable {
    *
    * If the fiber completes with [[Outcome.Succeeded]], the successful value is returned. If the
    * fiber completes with [[Outcome.Errored]], the error is raised. If the fiber completes with
-   * [[Outcome.Canceled]], the caller is indefinitely suspended without termination.
+   * [[Outcome.Canceled]], attempt to self-cancel, and if the self-cancelation fails, the caller
+   * is indefinitely suspended without termination.
    */
   def joinWithNever(implicit F: GenSpawn[F, E]): F[A] =
-    joinWith(F.never)
+    joinWith(F.canceled >> F.never)
 
   /**
    * Awaits the completion of the bound fiber and returns its result once it completes.

tests/shared/src/test/scala/cats/effect/IOSpec.scala

@@ -428,11 +428,20 @@ class IOSpec extends BaseSpec with Discipline with IOPlatformSpecification {
         } must completeAs(42)
       }
 
-      "joinWithNever on a canceled fiber" in ticked { implicit ticker =>
+      "joinWithNever on a canceled cancelable fiber" in ticked { implicit ticker =>
         (for {
           fib <- IO.sleep(2.seconds).start
           _ <- fib.cancel
           _ <- fib.joinWithNever
+        } yield ()) must selfCancel
+      }
+
+      "joinWithNever on a canceled uncancelable fiber" in ticked { implicit ticker =>
+        (for {
+          fib <- IO.never[Unit].uncancelable.start
+          _ <- IO.sleep(1.second)
+          _ <- fib.cancel
+          _ <- fib.joinWithNever
         } yield ()) must nonTerminate
       }