Fix pandas warning in sitemap harvester
When running tests, pandas currently issues a warning:
tests/test_sitemap_harvester.py::test_filter_urls
/local/home/a.pirogov/projects/data_harvesting/data_harvesting/harvester/sitemap.py:69: SettingWithCopyWarning:
A value is trying to be set on a copy of a slice from a DataFrame.
Try using .loc[row_indexer,col_indexer] = value instead
See the caveats in the documentation: https://pandas.pydata.org/pandas-docs/stable/user_guide/indexing.html#returning-a-view-versus-a-copy
sub_df['lastmod_date'] = pd.to_datetime(sub_df['lastmod']).dt.date
-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
That should be easy to fix and probably should be fixed to avoid breakage in the future (changes in pandas semantics etc. described in the linked docs pages).