Minor: rename test data file

compiler/testData/codegen/box/enum/openMethod.kt

@@ -0,0 +1,10 @@
+fun box() = IssueState.DEFAULT.ToString() + IssueState.FIXED.ToString()
+
+enum class IssueState {
+   DEFAULT
+   FIXED {
+       override fun ToString() = "K"
+   }
+
+   open fun ToString() : String = "O"
+}