Prepare debian changelog for 6.0-alpha1

Author: michaelsembwever

debian/changelog

@@ -1,8 +1,8 @@
-cassandra (6.0~alpha1) UNRELEASED; urgency=medium
+cassandra (6.0~alpha1) unstable; urgency=medium
 
   * New release
 
- -- Mick Semb Wever <mck@apache.org>  Wed, 21 Apr 2021 19:24:28 +0200
+ -- Mick Semb Wever <mck@apache.org>  Sat, 21 Mar 2026 23:45:40 +0100
 
 cassandra (5.0.4) unstable; urgency=medium