prepared corrected 6.4.x minor releases

Author: mkalkbrenner

CHANGELOG.md

@@ -4,17 +4,13 @@ All notable changes to the Solarium library will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
-## [Unreleased]
+## [6.4.0]
 ### Added
 - CBOR formatted update requests
 - Solarium\Core\Query\Helper::knn()
 - Solarium\Core\Query\Helper::knnTextToVector()
 - Solarium\Core\Query\Helper::vectorSimilarity()
 
-### Changed
-
-### Removed
-
 
 ## [6.3.7]
 ### Added