add some test cases

tests/ui/bytes_nth.fixed

@@ -1,9 +1,11 @@
 // run-rustfix
 
+#![allow(clippy::unnecessary_operation)]
 #![warn(clippy::bytes_nth)]
 
 fn main() {
-    let _ = "Hello".as_bytes().get(3);
-
-    let _ = String::from("Hello").as_bytes().get(3);
+    let s = String::from("String");
+    s.as_bytes().get(3);
+    &s.as_bytes().get(3);
+    s[..].as_bytes().get(3);
 }

tests/ui/bytes_nth.rs

@@ -1,9 +1,11 @@
 // run-rustfix
 
+#![allow(clippy::unnecessary_operation)]
 #![warn(clippy::bytes_nth)]
 
 fn main() {
-    let _ = "Hello".bytes().nth(3);
-
-    let _ = String::from("Hello").bytes().nth(3);
+    let s = String::from("String");
+    s.bytes().nth(3);
+    &s.bytes().nth(3);
+    s[..].bytes().nth(3);
 }

tests/ui/bytes_nth.stderr

@@ -1,16 +1,22 @@
-error: called `.byte().nth()` on a `str`
-  --> $DIR/bytes_nth.rs:6:13
+error: called `.byte().nth()` on a `String`
+  --> $DIR/bytes_nth.rs:8:5
    |
-LL |     let _ = "Hello".bytes().nth(3);
-   |             ^^^^^^^^^^^^^^^^^^^^^^ help: try calling `.as_bytes().get()`: `"Hello".as_bytes().get(3)`
+LL |     s.bytes().nth(3);
+   |     ^^^^^^^^^^^^^^^^ help: try: `s.as_bytes().get(3)`
    |
    = note: `-D clippy::bytes-nth` implied by `-D warnings`
 
 error: called `.byte().nth()` on a `String`
-  --> $DIR/bytes_nth.rs:8:13
+  --> $DIR/bytes_nth.rs:9:6
+   |
+LL |     &s.bytes().nth(3);
+   |      ^^^^^^^^^^^^^^^^ help: try: `s.as_bytes().get(3)`
+
+error: called `.byte().nth()` on a `str`
+  --> $DIR/bytes_nth.rs:10:5
    |
-LL |     let _ = String::from("Hello").bytes().nth(3);
-   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try calling `.as_bytes().get()`: `String::from("Hello").as_bytes().get(3)`
+LL |     s[..].bytes().nth(3);
+   |     ^^^^^^^^^^^^^^^^^^^^ help: try: `s[..].as_bytes().get(3)`
 
-error: aborting due to 2 previous errors
+error: aborting due to 3 previous errors