pre-commit: add isort hook and apply (#354)

tests/generate.py

@@ -1,10 +1,10 @@
 #!/usr/bin/env python
 import asyncio
 import os
-from pathlib import Path
 import platform
 import shutil
 import sys
+from pathlib import Path
 from typing import Set
 
 from tests.util import (
@@ -15,6 +15,7 @@ from tests.util import (
     protoc,
 )
 
+
 # Force pure-python implementation instead of C++, otherwise imports
 # break things because we can't properly reset the symbol database.
 os.environ["PROTOCOL_BUFFERS_PYTHON_IMPLEMENTATION"] = "python"