FE: split test "buildList type argument is inferred into upper bound"

Related to KT-50520, KT-56169

compiler/testData/diagnostics/testsWithStdLib/builderInference/buildListToUpperBound.kt

@@ -0,0 +1,11 @@
+// WITH_STDLIB
+// !LANGUAGE: -ForbidInferringPostponedTypeVariableIntoDeclaredUpperBound
+// ISSUE: KT-50520
+
+fun box(): String {
+    buildList {
+        val foo = { first() }
+        add(0, foo)
+    }
+    return "OK"
+}