[FIR] Fix FirDuplicateParameterNameInFunctionTypeChecker

It was supposed to check only function types...

Also note that it's probably impossible
to write a simpler test right now,
because we have a massive problem that
we ignore `FirTypeRef`s with `null`
sources despite having a dedicated
family of checkers for them
specifically. This will be fixed
separately as KT-65647.

^KT-65584 Fixed
^KT-65647

compiler/testData/diagnostics/tests/duplicateParameterNameSimplified.fir.kt

@@ -8,7 +8,7 @@ class MyTriple<T, K, M>(val a: T, val b: K, val c: M)
 
 fun test() {
     giveItName(10) {
-        MyTriple(it, it, it).also { <!DUPLICATE_PARAMETER_NAME_IN_FUNCTION_TYPE!>self<!> -> }
+        MyTriple(it, it, it).also { self -> }
         (duplicateIt(it) { a, b -> }).also { <!DUPLICATE_PARAMETER_NAME_IN_FUNCTION_TYPE!>function<!> -> }
     }
 }