Fix misleading test name

exercises/06_move_semantics/move_semantics4.rs

@@ -7,7 +7,7 @@ mod tests {
     // TODO: Fix the compiler errors only by reordering the lines in the test.
     // Don't add, change or remove any line.
     #[test]
-    fn move_semantics5() {
+    fn move_semantics4() {
         let mut x = 100;
         let y = &mut x;
         let z = &mut x;