Allow fn pointers comparisons lint in UI tests

tests/ui/function-pointer/function-pointer-comparison-issue-54685.rs

@@ -1,6 +1,8 @@
 //@ compile-flags: -C opt-level=3
 //@ run-pass
 
+#![allow(unpredictable_function_pointer_comparisons)]
+
 fn foo(_i: i32) -> i32 {
     1
 }