JS IR: mute codegen box tests automatically

compiler/testData/codegen/box/privateConstructors/synthetic.kt

@@ -1,3 +1,4 @@
+// IGNORE_BACKEND: JS_IR
 // TODO: muted automatically, investigate should it be ran for JS or not
 // IGNORE_BACKEND: JS, NATIVE
 

compiler/testData/codegen/box/privateConstructors/withArguments.kt

@@ -1,3 +1,4 @@
+// IGNORE_BACKEND: JS_IR
 // See also KT-6299
 public open class Outer private constructor(val s: String, val f: Boolean = true) {
     class Inner: Outer("xyz")

compiler/testData/codegen/box/privateConstructors/withDefault.kt

@@ -1,3 +1,4 @@
+// IGNORE_BACKEND: JS_IR
 // See also KT-6299
 public open class Outer private constructor(val x: Int = 0) {
     class Inner: Outer()

compiler/testData/codegen/box/privateConstructors/withLinkedClasses.kt

@@ -1,3 +1,4 @@
+// IGNORE_BACKEND: JS_IR
 // See also KT-6299
 public open class Outer private constructor(val p: Outer?) {
     object First: Outer(null)