Rollup merge of #116223 - catandcoder:master, r=cjgillot

Fix misuses of a vs an

Fixes the misuse of "a" vs "an", according to English grammatical
expectations and using https://www.a-or-an.com/

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -1364,7 +1364,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                     err.note(format!(
                         "a for loop advances the iterator for you, the result is stored in `{loop_bind}`."
                     ));
-                    err.help("if you want to call `next` on a iterator within the loop, consider using `while let`.");
+                    err.help("if you want to call `next` on an iterator within the loop, consider using `while let`.");
         }
     }