Fix changelog

Author: cbourjau

CHANGELOG.rst

@@ -10,6 +10,11 @@ Change log
 0.14.0 (2025-06-03)
 -------------------
 
+**Breaking change**
+
+- The :func:`spox.opset.ai.onnx.v18.group_normalization` constructor function and its re-exports in :mod:`spox.opset.ai.onnx.v19`, :mod:`spox.opset.ai.onnx.v20` have been removed due to it being deprecated upstream.
+
+
 **Bug fix**
 
 - Adds missing shape inference logic for :func:`spox.opsets.ai.v19.loop` and :func:`spox.opsets.ai.v21.loop`.