release: Bump version to 0.5.6 (#502)

Co-authored-by: GitHub Action <action@github.com>

Author: github-actions[bot]

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "openpipe-art"
-version = "0.5.5"
+version = "0.5.6"
 description = "The OpenPipe Agent Reinforcement Training (ART) library"
 readme = "README.md"
 requires-python = ">=3.11"