Add v1.2.1 changelog

CHANGELOG.md

+## [v1.2.1](https://git.duniter.org/clients/python/duniterpy/-/milestones/22) (26th March 2025)
+
+### Python versions
+
+- #208, !198: Add support for Python v3.13
+  - !199: Fix `API.request_url()` with Py3.13
+- #199, !198: Drop Python v3.8 support
+
+### DevEnv
+
+- #215, !202: Migrate to Poetry v2
+
+### Project
+
+- #205, !201: Update copyright to 2025
+
 ## [v1.2.0](https://git.duniter.org/clients/python/duniterpy/-/milestones/20) (31st January 2024)
 
 ### Code