ci: Prepare release of version 3.1.1 (#139)

* Update CHANGELOG.rst

* Bump version

* Pin treebeard for Django CMS 3.7 tests

* Update dj30_cms37.txt

Author: fsbraun

CHANGELOG.rst

@@ -2,8 +2,10 @@
 Changelog
 =========
 
-Unreleased
-==========
+3.1.1
+=====
+
+* fix: Removed tight django-treebeard restriction added when 4.5.0 contained breaking changes. The core CMS and django-treebeard have since been patched to resolve the issue.
 
 4.1.0 (2024-05-16)
 ==================
@@ -66,7 +68,6 @@ Unreleased
 
 * Add support for ace editor loaded from static files through djangocms-static-ace
 * Add dark mode support
-* fix: Removed tight django-treebeard restriction added when 4.5.0 contained breaking changes. The core CMS and django-treebeard have since been patched to resolve the issue.
 
 3.0.0 (2020-09-02)
 ==================