fix: add scalatestplus-testng dep and Dispatcher[Task] for reactive-streams TCK

The reactive-streams TCK tests require scalatestplus-testng for the
TestNG/ScalaTest bridge, and CE3's Iterant.toReactivePublisher now
requires an implicit Dispatcher[Task].

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: halotukozak

build.sbt

@@ -705,7 +705,8 @@ lazy val reactiveTests = project
   .dependsOn(reactiveJVM, tailJVM)
   .settings(
     libraryDependencies ++= Seq(
-      reactiveStreamsTCKLib % Test
+      reactiveStreamsTCKLib % Test,
+      "org.scalatestplus" %% "testng-7-5" % "3.2.17.0" % Test
     )
   )
 

reactiveTests/src/test/scala/monix/reactiveTests/IterantToPublisherTest.scala

@@ -18,6 +18,8 @@
 package monix.reactiveTests
 
 import cats.effect.Sync
+import cats.effect.std.Dispatcher
+import cats.effect.unsafe.implicits.{global => ioRuntime}
 import monix.execution.Scheduler.Implicits.global
 import monix.eval.Task
 import monix.execution.exceptions.DummyException
@@ -33,6 +35,15 @@ import scala.util.Random
 class IterantToPublisherTest extends PublisherVerification[Long](env())
   with TestNGSuiteLike {
 
+  // CE3 Dispatcher[Task] required for toReactivePublisher
+  implicit val taskDispatcher: Dispatcher[Task] = new Dispatcher[Task] {
+    import monix.execution.Scheduler.Implicits.global as s
+    def unsafeToFutureCancelable[A](fa: Task[A]): (scala.concurrent.Future[A], () => scala.concurrent.Future[Unit]) = {
+      val cf = fa.runToFuture(s)
+      (cf, () => { cf.cancel(); scala.concurrent.Future.successful(()) })
+    }
+  }
+
   def createPublisher(elements: Long): Publisher[Long] = {
     if (elements < 4096) {
       val list: List[Long] = (0 until elements.toInt).map(_.toLong).toList