Use env_dir accessor

Author: akx

src/tox/tox_env/package.py

@@ -67,7 +67,7 @@ def __getattribute__(self, name: str) -> Any:
 
     def register_config(self) -> None:
         super().register_config()
-        file_lock_path: Path = self.conf["env_dir"] / "file.lock"
+        file_lock_path: Path = self.env_dir / "file.lock"
         self._file_lock = FileLock(file_lock_path)
         file_lock_path.parent.mkdir(parents=True, exist_ok=True)
         self.core.add_config(