Minor. Fix tests after CoroutineContext introduction

compiler/testData/codegen/bytecodeText/constCoroutine.kt

@@ -20,6 +20,7 @@ fun box(): String {
     return "OK"
 }
 
-// 2 GETSTATIC kotlin/Unit.INSTANCE : Lkotlin/Unit;
-// 1 GETSTATIC EmptyContinuation.INSTANCE
-// 3 GETSTATIC
+// 2 GETSTATIC kotlin/Unit.INSTANCE
+// 1 GETSTATIC EmptyContinuation.Companion
+// 3 GETSTATIC kotlin\/coroutines\/EmptyCoroutineContext.INSTANCE
+// 6 GETSTATIC

compiler/testData/codegen/java8/box/async.kt

@@ -48,6 +48,8 @@ fun box(): String {
 fun <T> async(c: suspend () -> T): CompletableFuture<T> {
     val future = CompletableFuture<T>()
     c.startCoroutine(object : Continuation<T> {
+        override val context = EmptyCoroutineContext
+
         override fun resume(data: T) {
             future.complete(data)
         }

compiler/testData/codegen/java8/box/asyncException.kt

@@ -45,6 +45,8 @@ fun box(): String {
 fun <T> async(c: suspend () -> T): CompletableFuture<T> {
     val future = CompletableFuture<T>()
     c.startCoroutine(object : Continuation<T> {
+        override val context = EmptyCoroutineContext
+        
         override fun resume(data: T) {
             future.complete(data)
         }