[test] Mute failing irText tests

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

@@ -1,4 +1,6 @@
 // WITH_STDLIB
+// IGNORE_BACKEND_K2: JS_IR
+// IGNORE_BACKEND_K2: JS_IR_ES6
 // !LANGUAGE: +ImplicitSignedToUnsignedIntegerConversion
 
 // FILE: signedToUnsignedConversions_annotation.kt
@@ -53,4 +55,4 @@ fun test() {
 
 //    such kind of conversions (Int <-> Long) actually are not supported
 //    takeLong(IMPLICIT_INT)
-}
+}