extend single_element_loop to match .iter()

tests/ui/single_element_loop.fixed

@@ -8,4 +8,9 @@ fn main() {
         let item = &item1;
         println!("{}", item);
     }
+
+    {
+        let item = &item1;
+        println!("{:?}", item);
+    }
 }

tests/ui/single_element_loop.rs

@@ -7,4 +7,8 @@ fn main() {
     for item in &[item1] {
         println!("{}", item);
     }
+
+    for item in [item1].iter() {
+        println!("{:?}", item);
+    }
 }

tests/ui/single_element_loop.stderr

@@ -15,5 +15,21 @@ LL |         println!("{}", item);
 LL |     }
    |
 
-error: aborting due to previous error
+error: for loop over a single element
+  --> $DIR/single_element_loop.rs:11:5
+   |
+LL | /     for item in [item1].iter() {
+LL | |         println!("{:?}", item);
+LL | |     }
+   | |_____^
+   |
+help: try
+   |
+LL |     {
+LL |         let item = &item1;
+LL |         println!("{:?}", item);
+LL |     }
+   |
+
+error: aborting due to 2 previous errors