Rollup merge of rust-lang#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/

Author: workingjubilee

alloc/src/collections/btree/dedup_sorted_iter.rs

@@ -1,6 +1,6 @@
 use core::iter::Peekable;
 
-/// A iterator for deduping the key of a sorted iterator.
+/// An iterator for deduping the key of a sorted iterator.
 /// When encountering the duplicated key, only the last key-value pair is yielded.
 ///
 /// Used by [`BTreeMap::bulk_build_from_sorted_iter`][1].