update changelog

Signed-off-by: Thibault Mange <22740367+thibaultmg@users.noreply.github.com>

CHANGELOG.md

@@ -23,6 +23,7 @@ We use *breaking :warning:* to mark changes that are not backward compatible (re
 - [#6352](https://github.com/thanos-io/thanos/pull/6352) Store: Expose store gateway query stats in series response hints.
 - [#6420](https://github.com/thanos-io/thanos/pull/6420) Index Cache: Cache expanded postings.
 - [#6441](https://github.com/thanos-io/thanos/pull/6441) Compact: Compactor will set `index_stats` in `meta.json` file with max series and chunk size information.
+- [#6467](https://github.com/thanos-io/thanos/pull/6467) Receive mixin: Add alert for tenant reaching head series limit.
 
 ### Fixed
 - [#6456](https://github.com/thanos-io/thanos/pull/6456) Store: fix crash when computing set matches from regex pattern