update changelog

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

CHANGELOG.md

@@ -24,6 +24,7 @@ We use *breaking :warning:* to mark changes that are not backward compatible (re
 - [#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.
 - [#6466](https://github.com/thanos-io/thanos/pull/6466) Mixin (Receive): add limits alerting for configuration reload and meta-monitoring.
+- [#6467](https://github.com/thanos-io/thanos/pull/6467) Mixin (Receive): 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