[FIR] Report errors for upper bounded type variables by an empty intersection type

^KT-51221 Fixed

compiler/testData/diagnostics/tests/inference/coercionToUnit/coercionToUnitWithNothingType.fir.kt

@@ -47,7 +47,7 @@ fun test(i: Inv<Nothing>, iUnit: Inv<Unit>) {
 
     if (iUnit is String) {
         launch {
-            run(A.flexible(iUnit)) { 42 }
+            run(A.<!INFERRED_TYPE_VARIABLE_INTO_EMPTY_INTERSECTION!>flexible<!>(iUnit)) { 42 }
         }
     }
 }