CHANGES: Comment on ci python version

Author: tony

CHANGES

@@ -8,6 +8,7 @@ Here you can find the recent changes to libtmux
 - #324: Update poetry to 1.1
   - CI: Use poetry 1.1.7 and `install-poetry.py` installer
   - Relock poetry.lock at 1.1 (w/ 1.1.7's fix)
+- #339 (CI): Lock python at 3.9 to avoid poetry issue with `dataclasses`
 
 ## libtmux 0.10.1 (2021-06-16)
 - Update `Window.select_window()` for #271