Update fn_once-moved test

Author: tommyip

src/test/ui/fn_once-moved.rs

@@ -20,5 +20,6 @@ fn main() {
     debug_dump_dict();
     debug_dump_dict();
     //~^ ERROR use of moved value: `debug_dump_dict`
-    //~| NOTE closure was moved because it only implements `FnOnce`
+    //~| NOTE closure cannot be invoked more than once because it moves the
+    //~| variable `dict` out of its environment
 }

src/test/ui/fn_once-moved.stderr

@@ -1,12 +1,15 @@
 error[E0382]: use of moved value: `debug_dump_dict`
   --> $DIR/fn_once-moved.rs:21:5
    |
+16 |         for (key, value) in dict {
+   |                             ---- dict moved here
+...
 20 |     debug_dump_dict();
    |     --------------- value moved here
 21 |     debug_dump_dict();
    |     ^^^^^^^^^^^^^^^ value used here after move
    |
-   = help: closure was moved because it only implements `FnOnce`
+   = help: closure cannot be invoked more than once because it moves the variable `dict` out of its environment
 
 error: aborting due to previous error