Fix ParallelTesting code

Author: odersky

compiler/test/dotty/tools/vulpix/ParallelTesting.scala

@@ -12,7 +12,7 @@ import java.nio.file.{Files, NoSuchFileException, Path, Paths}
 import java.nio.charset.{Charset, StandardCharsets}
 import java.text.SimpleDateFormat
 import java.util.{HashMap, Timer, TimerTask}
-import java.util.concurrent.{TimeUnit, TimeoutException, Executors => JExecutors}
+import java.util.concurrent.{TimeUnit, TimeoutException, Future, Executors => JExecutors}
 
 import scala.collection.mutable
 import scala.io.{Codec, Source}
@@ -654,7 +654,7 @@ trait ParallelTesting extends RunnerOrchestration { self =>
           throw new TimeoutException(s"Compiling targets timed out, remaining targets: ${remaining.mkString(", ")}")
         end if
 
-        for fut <- eventualResults do
+        for fut: Future[?] <- eventualResults do
           try fut.get()
           catch case ex: Exception =>
             System.err.println(ex.getMessage)