fix(deps): update dependency isort to v6 (#49)

Author: renovate-bot

pyproject.toml

@@ -39,7 +39,7 @@ Changelog = "https://github.com/googleapis/genai-toolbox-langchain-python/blob/m
 [project.optional-dependencies]
 test = [
     "black[jupyter]==25.1.0",
-    "isort==5.13.2",
+    "isort==6.0.1",
     "mypy==1.13.0",
     "pytest-asyncio==0.24.0",
     "pytest==8.3.3",