Skip instability meta tests on Windows

Author: liufengyun

Diff for: compiler/test/dotty/tools/vulpix/VulpixUnitTests.scala

@@ -83,7 +83,7 @@ class VulpixUnitTests extends ParallelTesting {
   @Test def deadlock: Unit =
     compileFile("tests/vulpix-tests/unit/deadlock.scala", defaultOptions).expectFailure.checkRuns()
 
-  @Test def badJava: Unit =
+  @Test def badJava: Unit = if (!scala.util.Properties.isWin)
     try {
       compileFile("tests/vulpix-tests/unit/BadJava.java", defaultOptions).suppressAllOutput.checkCompile()
       fail()