[FIR] Check is for impossibility

^KT-58203 Fixed
^KT-62646

compiler/testData/diagnostics/testsWithStdLib/contracts/smartcasts/intersectingInfo.fir.kt

@@ -45,8 +45,8 @@ fun intersectingInfo2(x: Any?, y: Any?) {
     // of them is absent in each arg of "||"-operator, so they *shouldn't* lead to smartcast
 
     if ((isString(x) && !notIsInt(x) && y is String) ||
-        (!notIsString(x) && isString(y) && y is Int) ||
-        (x is String && !notIsInt(y) && x is Int)) {
+        (!notIsString(x) && isString(y) && <!USELESS_IS_CHECK!>y is Int<!>) ||
+        (x is String && !notIsInt(y) && <!USELESS_IS_CHECK!>x is Int<!>)) {
         x.length
         x.<!UNRESOLVED_REFERENCE!>inc<!>()
         y.<!UNRESOLVED_REFERENCE!>length<!>