apply isort globally

swh/loader/svn/converters.py

swh/loader/svn/directory.py

swh/loader/svn/loader.py

swh/loader/svn/replay.py

swh/loader/svn/svn_repo.py

swh/loader/svn/tasks.py

swh/loader/svn/tests/conftest.py

swh/loader/svn/tests/test_converters.py

swh/loader/svn/tests/test_directory.py

swh/loader/svn/tests/test_externals.py

swh/loader/svn/tests/test_loader.py

swh/loader/svn/tests/test_svn_retry.py

swh/loader/svn/tests/test_task.py

swh/loader/svn/tests/test_task_directory.py

swh/loader/svn/tests/test_utils.py