Fix changelog headers (#531)

* Remove a duplicate version header from the changelog

Co-authored-by: Jonathan Shook <[email protected]>

Author: jshook

CHANGELOG.md

@@ -4,8 +4,6 @@ All notable changes to this project will be documented in this file. Dates are d
 
 Generated by [`auto-changelog`](https://github.com/CookPete/auto-changelog).
 
-#### [4.0.0-rc.3](https://github.com/datastax/jvector/compare/4.0.0-rc.3...4.0.0-rc.3)
-
 #### [4.0.0-rc.3](https://github.com/datastax/jvector/compare/4.0.0-rc.2...4.0.0-rc.3)
 
 > 19 September 2025