JVM IR: Avoid direct invokes in callable reference tests

Due to the direct invoke optimization, most callable reference tests
were not generating callable references/lambdas.

compiler/testData/codegen/box/jvm8/defaults/callableReference.kt

@@ -12,7 +12,7 @@ interface Test {
         get() = "K"
 
     fun test(): String {
-        return (::foo)() + (::bar)()
+        return (::foo).let { it() } + (::bar).let { it() }
     }
 }