revert workaround change for scala/scala3#8425 (fixed)

Author: giabao

akka-testkit/src/test/scala/akka/testkit/WithLogCapturing.scala

@@ -50,12 +50,10 @@ trait WithLogCapturing extends SuiteMixin { this: TestSuite =>
   /** Adds a prefix to every line printed out during execution of the thunk. */
   private def withPrefixedOut[T](prefix: String)(thunk: => T): T = {
     val oldOut = Console.out
-    // https://github.com/lampepfl/dotty/issues/8425
-    val os = new OutputStream {
-      override def write(b: Int): Unit = oldOut.write(b)
-    }
     val prefixingOut =
-      new PrintStream(os) {
+      new PrintStream(new OutputStream {
+        override def write(b: Int): Unit = oldOut.write(b)
+      }) {
         override def println(x: Any): Unit =
           oldOut.println(prefix + String.valueOf(x).replaceAllLiterally("\n", s"\n$prefix"))
       }