directory: Ensure to filter out .hg dirs in HgCheckoutLoader
requested to merge anlambert/swh-loader-mercurial:hg-checkout-loader-filter-out-.hg-dirs into master
Those are mercurial related and should not end up in the directory archived by that loader.
Related to swh/infra/sysadm-environment#5256 (closed).
Tests were not updated as they are done by swh-loader-core in swh-loader-core!517 (merged).