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/jvmStatic/functionReference.kt

@@ -10,4 +10,4 @@ object O {
 
 // FILE: u2.kt
 
-fun box() = (O::foo)()
+fun box() = (O::foo).let { it() }