Replace 'Thread.ofVirtual().start()' with 'Thread.startVirtualThread(…

…)' (#907)

There's no need to use the builder when all we need is to simply start a `Thread`

src/main/java/com/pivovarit/collectors/Dispatcher.java

@@ -61,7 +61,7 @@ static <T> Dispatcher<T> virtual(int permits) {
 
     void start() {
         if (!started.getAndSet(true)) {
-            Thread.ofVirtual().start(() -> {
+            Thread.startVirtualThread(() -> {
                 try {
                     while (true) {
                         try {