[tests] Do not use test_family for tests
[tests] Do not use test_family for tests

test_family is deprecated in favour of wikipedia:test

- use "wikipedia" instead of "test" for *_obsolete_readonly tests
- use subTest with  test_family_load_valid
- suppress warning for deprecated test_family in test_family_load_valid

Bug: T228375
Change-Id: Idb572837fc364579c2ba1e4ca20344afeea7d06e

wikimedia/pywikibot-core,PersianWikipedia/pywikibot-core,wikimedia/pywikibot-core