Properly close file

Otherwise, we encounter the following error on windows:

java.nio.file.FileSystemException: out\rewrites\i8982\rewrites\i8982\i8982.scala: The process cannot access the file because it is being used by another process.
	at sun.nio.fs.WindowsException.translateToIOException(WindowsException.java:86)
	at sun.nio.fs.WindowsException.rethrowAsIOException(WindowsException.java:97)
	at sun.nio.fs.WindowsException.rethrowAsIOException(WindowsException.java:102)
	at sun.nio.fs.WindowsFileSystemProvider.implDelete(WindowsFileSystemProvider.java:269)
	at sun.nio.fs.AbstractFileSystemProvider.delete(AbstractFileSystemProvider.java:103)
	at java.nio.file.Files.delete(Files.java:1126)
	at dotty.tools.vulpix.ParallelTesting$CompilationTest.delete(ParallelTesting.scala:1061)
	at dotty.tools.vulpix.ParallelTesting$CompilationTest.delete$$anonfun$2(ParallelTesting.scala:1060)
	at dotty.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at dotty.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.ArrayOps$.foreach$extension(ArrayOps.scala:1323)
	at dotty.tools.vulpix.ParallelTesting$CompilationTest.delete(ParallelTesting.scala:1060)
	at dotty.tools.vulpix.ParallelTesting$CompilationTest.delete$$anonfun$1(ParallelTesting.scala:1057)
	at dotty.runtime.function.JProcedure1.apply(JProcedure1.java:15)
	at dotty.runtime.function.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.immutable.List.foreach(List.scala:333)
	at dotty.tools.vulpix.ParallelTesting$CompilationTest.delete(ParallelTesting.scala:1057)
	at dotty.tools.vulpix.ParallelTesting$CompilationTest.cleanup(ParallelTesting.scala:985)
	at dotty.tools.vulpix.ParallelTesting$CompilationTest.checkCompile(ParallelTesting.scala:892)
	at dotty.tools.vulpix.ParallelTesting$RewriteTest.verifyOutput(ParallelTesting.scala:614)
	at dotty.tools.vulpix.ParallelTesting$RewriteTest.onSuccess(ParallelTesting.scala:618)
	at dotty.tools.vulpix.ParallelTesting$CompilationLogic.dotty$tools$vulpix$ParallelTesting$CompilationLogic$$onComplete(ParallelTesting.scala:275)
	at dotty.tools.vulpix.ParallelTesting$$anon$2.checkTestSource$$anonfun$1(ParallelTesting.scala:264)
	at dotty.runtime.function.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:12)
	at dotty.tools.vulpix.ParallelTesting$Test.tryCompile(ParallelTesting.scala:431)
	at dotty.tools.vulpix.ParallelTesting$$anon$2.checkTestSource(ParallelTesting.scala:266)
	at dotty.tools.vulpix.ParallelTesting$Test$LoggedRunnable.run(ParallelTesting.scala:334)
	at dotty.tools.vulpix.ParallelTesting$Test$LoggedRunnable.run$(ParallelTesting.scala:316)
	at dotty.tools.vulpix.ParallelTesting$$anon$2.run(ParallelTesting.scala:261)

Author: liufengyun

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

@@ -606,7 +606,12 @@ trait ParallelTesting extends RunnerOrchestration { self =>
       testSource.sourceFiles.foreach { file =>
         if checkFiles.contains(file) then
           val checkFile = checkFiles(file)
-          val actual = Source.fromFile(file, "UTF-8").getLines().toList
+          val actual = {
+            val source = Source.fromFile(file, "UTF-8")
+            val lines  = source.getLines().toList
+            source.close()
+            lines
+          }
           diffTest(testSource, checkFile, actual, reporters, logger)
       }