Update isort dependency for Python version compatibility

Author: dishaprakash

pyproject.toml

@@ -39,7 +39,8 @@ Changelog = "https://github.com/googleapis/llama-index-cloud-sql-pg-python/blob/
 [project.optional-dependencies]
 test = [
     "black[jupyter]==25.9.0",
-    "isort==6.1.0",
+    "isort==6.1.0; python_version == '3.9'",
+    "isort==7.0.0; python_version >= '3.10'",
     "mypy==1.18.2",
     "pytest-asyncio==1.2.0",
     "pytest==8.4.2",