[FIR] Fix tests (ARGUMENT_TYPE_MISMATCH instead of INCOMPATIBLE_CANDIDATE)

compiler/testData/diagnostics/tests/explicitDefinitelyNotNull/simple.fir.kt

@@ -4,7 +4,7 @@ fun <T> foo(x: T, y: T!!): T!! = x ?: y
 
 fun main() {
     foo<String>("", "").length
-    <!INAPPLICABLE_CANDIDATE!>foo<!><String>("", null).length
+    foo<String>("", <!ARGUMENT_TYPE_MISMATCH!>null<!>).length
     foo<String?>(null, "")<!UNSAFE_CALL!>.<!>length
     foo<String?>(null, null)<!UNSAFE_CALL!>.<!>length