Fix typo in release notes

Author: rustagir

source/reference/release-notes.txt

@@ -31,7 +31,7 @@ Learn what's new in:
 What's New in 2.22
 ------------------
 
-The {+driver-short+} 2.21 release includes the following new features: 
+The {+driver-short+} 2.22 release includes the following new features: 
 
 - Adds the ``type`` parameter to the
   ``Mongo::SearchIndex::View#create_one`` and