mypy: Fix errors with release >= v0.900

requirements-test.txt

-Click
+click
 pytest
 pytz
+types-python-dateutil
+types-pytz

swh/__init__.py

 from pkgutil import extend_path
-from typing import Iterable
+from typing import List
 
-__path__ = extend_path(__path__, __name__)  # type: Iterable[str]
+__path__: List[str] = extend_path(__path__, __name__)