docs(CHANGES): Note gp-libs addition to test dep group

Author: tony

CHANGES

@@ -19,6 +19,10 @@ $ pipx install --suffix=@next 'tmuxp' --pip-args '\--pre' --force
 
 <!-- Maintainers, insert changes / features for the next release here -->
 
+### Packaging
+
+- pypoetry: Add `gp-lib` to `test` dependency group
+
 ## tmuxp 1.32.0 (2023-11-19)
 
 _Maintenance only, no bug fixes or new features_