Add false positive test for using different Vec's length

Currently failing, so currently commented out.

Author: HarrisonMc555

tests/ui/use_last.rs

@@ -18,10 +18,19 @@ fn index_into_last() -> i32 {
     last_element + 1 // To avoid warnings
 }
 
+// False positive test (currently failing)
+// fn use_last_with_different_vec_length() -> Option<i32> {
+//     let x = vec![2, 3, 5];
+//     let y = vec!['a', 'b', 'c'];
+//     let last_element = x.get(y.len() - 1);
+//     last_element.map(|val| val + 1)
+// }
+
 fn main() {
     let expected_value: i32 = 6;
     println!("Working...");
     assert_eq!(dont_use_last(), Some(expected_value));
     assert_eq!(indexing_two_from_end(), Some(expected_value));
     assert_eq!(index_into_last(), expected_value);
+    // assert_eq!(use_last_with_different_vec_length(), Some(expected_value));
 }