add changelog

Author: sdetweil

CHANGELOG.md

@@ -23,6 +23,10 @@ planned for 2025-07-01
 - [workflow] Run linter und spellcheck with LTS node version (#3767)
 - [workflow] Split "Run test" step into two steps for more clarity (#3767)
 
+### Fixed
+
+- [calendar] fix fullday event rrule until with timezone offset (#3781)
+
 ## [2.31.0] - 2025-04-01
 
 Thanks to: @Developer-Incoming, @eltociear, @geraki, @khassel, @KristjanESPERANTO, @MagMar94, @mixasgr, @n8many, @OWL4C, @rejas, @savvadam, @sdetweil.