Make the output a list to be able to consume it twice

Some modifications to the code made it an iterator. The checks where performed
correctly but the output for the diff where empty.

Author: nicolasstucki

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

@@ -537,7 +537,7 @@ trait ParallelTesting extends RunnerOrchestration { self =>
                     val output = Source.fromFile(outDir.getParent + "_decompiled" + JFile.separator + outDir.getName
                       + JFile.separator + "decompiled.scala").getLines().map {line =>
                       stripTrailingWhitespaces.unapplySeq(line).map(_.head).getOrElse(line)
-                    }
+                    }.toList
 
                     val check: String = Source.fromFile(checkFile).getLines().filter(!_.startsWith(ignoredFilePathLine))
                       .mkString("\n")