add nll stderr

Author: csmoe

src/test/ui/suggestions/issue-51244.nll.stderr

@@ -0,0 +1,11 @@
+error[E0594]: cannot assign to data in a `&` reference
+  --> $DIR/issue-51244.rs:13:5
+   |
+LL |     let ref my_ref @ _ = 0;
+   |         -------------- help: consider changing this to be a mutable reference: `&mut ef my_ref @ _`
+LL |     *my_ref = 0; //~ ERROR cannot assign to immutable borrowed content `*my_ref` [E0594]
+   |     ^^^^^^^^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0594`.