FIR: Fix exception on remaining flexible ILT in lambda

^KT-49191 Related

compiler/testData/codegen/box/fir/flexibleIntegerLiterals.kt

@@ -0,0 +1,18 @@
+// TARGET_BACKEND: JVM
+// IGNORE_BACKEND: JVM, JVM_IR, ANDROID, ANDROID_IR
+// IGNORE_LIGHT_ANALYSIS
+// WITH_RUNTIME
+// FULL_JDK
+
+// This test fails on FE 1.0, but works in production compiler (see KT-49191):
+// Caused by: java.lang.AssertionError: Lower bound Function<in (String..String?), out (IntegerLiteralType[Int,Long,Byte,Short]..IntegerLiteralType[Int,Long,Byte,Short]?)> of a flexible type must be a subtype of the upper bound Function<in (String..String?), out (IntegerLiteralType[Int,Long,Byte,Short]..IntegerLiteralType[Int,Long,Byte,Short]?)>?
+// at org.jetbrains.kotlin.types.FlexibleTypeImpl.runAssertions(flexibleTypes.kt:105)
+fun box(): String {
+    val x = Comparator.comparing { x: String ->
+        1
+    }
+
+    if (x.compare("O", "K") != 0) return "fail"
+
+    return "OK"
+}