Changed extension in parsing test data (jet -> kt)

compiler/testData/psi/examples/Stack.kt

@@ -0,0 +1,13 @@
+class Stack<T> : IPushPop<T> {
+  private val data = ArrayList<T>();
+
+  override fun push(item : T) {
+    data.add(item) // Problem: I would like to write push(...) = data.add(...), but the types do not match
+  }
+
+  override fun pop() = data.removeLast()
+
+  override val isEmpty
+    get() = data.isEmpty
+
+}