Generate min/max constants as non-const in ranges tests

in order to make them appear as unknown values to codegen.

compiler/testData/codegen/box/ranges/unsigned/expression/progressionMaxValueMinusTwoToMaxValue.kt

@@ -3,10 +3,10 @@
 // WITH_RUNTIME
 
 
-const val MaxUI = UInt.MAX_VALUE
-const val MaxUB = UByte.MAX_VALUE
-const val MaxUS = UShort.MAX_VALUE
-const val MaxUL = ULong.MAX_VALUE
+val MaxUI = UInt.MAX_VALUE
+val MaxUB = UByte.MAX_VALUE
+val MaxUS = UShort.MAX_VALUE
+val MaxUL = ULong.MAX_VALUE
 
 fun box(): String {
     val list1 = ArrayList<UInt>()