[test] Mute failing irText tests

compiler/testData/ir/irText/expressions/smartCasts.kt

@@ -1,5 +1,7 @@
 // FIR_IDENTICAL
 // WITH_STDLIB
+// IGNORE_BACKEND_K2: JS_IR
+// IGNORE_BACKEND_K2: JS_IR_ES6
 
 fun expectsString(s: String) {}
 fun expectsInt(i: Int) {}
@@ -23,4 +25,4 @@ fun test2(x: Any): String {
 fun test3(x: Any): String {
     if (x !is String) return ""
     return x
-}
+}