Fix a comment

Author: oli-obk

src/test/ui/consts/partial_qualif.rs

@@ -4,7 +4,7 @@ use std::cell::Cell;
 
 const FOO: &(Cell<usize>, bool) = {
     let mut a = (Cell::new(0), false);
-    a.1 = true; // resets `qualif(a)` to `qualif(true)`
+    a.1 = true; // sets `qualif(a)` to `qualif(a) | qualif(true)`
     &{a} //~ ERROR cannot borrow a constant which may contain interior mutability
 };