Fix padding

Author: nicolasstucki

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

@@ -511,7 +511,7 @@ trait ParallelTesting extends RunnerOrchestration { self =>
 
           if (outputLines.length != checkLines.length || !linesMatch) {
             // Print diff to files and summary:
-            val expectedSize = DiffUtil.EOF.length max outputLines.map(_.length).max
+            val expectedSize = DiffUtil.EOF.length max checkLines.map(_.length).max
             val diff = outputLines.padTo(checkLines.length, "").zip(checkLines.padTo(outputLines.length, "")).map { case (act, exp) =>
               DiffUtil.mkColoredLineDiff(exp, act, expectedSize)
             }.mkString("\n")