Fix scala-js/scala-js#3412: Throw an IOException in noThrowOnBadFileTest

This makes sure no Scala version regard the failure as
fatal (NotImplementedError was considered fatal in 2.10). Also it
simply makes much more sense.

Author: gzm0

js-envs-test-kit/src/main/scala/org/scalajs/jsenv/test/RunTests.scala

@@ -118,10 +118,12 @@ private[test] class RunTests(config: JSEnvSuiteConfig, withCom: Boolean) {
 
   @Test
   def noThrowOnBadFileTest: Unit = {
+    def fail() = throw new java.io.IOException("exception for test")
+
     val badFile = new VirtualBinaryFile {
-      def path: String = ???
-      def exists: Boolean = ???
-      def inputStream: java.io.InputStream = ???
+      def path: String = fail()
+      def exists: Boolean = fail()
+      def inputStream: java.io.InputStream = fail()
     }
 
     // `start` may not throw but must fail asynchronously