[IR] Restore and fix ifConstVal test

It was accidentally dropped after KT-55196 fix.

compiler/testData/diagnostics/tests/modifiers/const/ifConstVal_after.fir.kt

@@ -4,19 +4,19 @@ const val flag = true
 const val value = 10
 
 const val condition = if (flag) "True" else "Error"
-const val withWhen = <!CONST_VAL_WITH_NON_CONST_INITIALIZER!>when (flag) {
+const val withWhen = when (flag) {
     true -> "True"
     else -> "Error"
-}<!>
+}
 const val withWhen2 = when {
     flag == true -> "True"
     else -> "Error"
 }
-const val withWhen3 = <!CONST_VAL_WITH_NON_CONST_INITIALIZER!>when(value) {
+const val withWhen3 = when(value) {
     10 -> "1"
     100 -> "2"
     else -> "3"
-}<!>
+}
 const val multibranchIf = if (value == 100) 1 else if (value == 1000) 2 else 3
 
 val nonConstFlag = true