Update changelog with summary statement regarding minor breaking change

Author: ArBridgeman

doc/changes/unreleased.md

@@ -1,5 +1,16 @@
 # Unreleased
 
+## Summary
+
+From exasol-toolbox version ``1.0.0`` the default behavior for ``.github/actions/python-environment/action.yml``
+has changed. In previous versions, the default value for ``poetry-version`` was ``1.2.2``,
+and it is now ``2.1.2``. 
+
+* Depending on its poetry version, a repository relying on the default behavior of said 
+action may run into breaking changes. This can easily be resolved with explicitly setting the
+`poetry-version` when calling the GitHub action. It is, however, recommended whenever
+possible to update the poetry version of affected repository to ``2.x``.
+
 ## ✨ Features
 
 * [#73](https://github.com/exasol/python-toolbox/issues/73): Added nox target for auditing work spaces in regard to known vulnerabilities
@@ -8,5 +19,5 @@
 * [#372](https://github.com/exasol/python-toolbox/issues/372): Added conversion from pip-audit JSON to expected GitHub Issue format
 
 ## ⚒️ Refactorings
-* [#388](https://github.com/exasol/python-toolbox/issues/388): Switch GitHub workflows to use pinned OS version
-* [#376](https://github.com/exasol/python-toolbox/issues/376): Update to poetry 2.1.2
+* [#388](https://github.com/exasol/python-toolbox/issues/388): Switched GitHub workflows to use pinned OS version
+* [#376](https://github.com/exasol/python-toolbox/issues/376): Updated to poetry ``2.1.2``