Fixed incorrect filter name in docs/topics/i18n/translation.txt.
Fixed #23956 -- Fixed migration creation for multiple table inheritance
Fixed typo in admin deprecation message.
Fixed #23977 -- Added setdefault() method to HttpResponse
Appeased spell checker.
Cleanup cache in contrib.sites to prevent test interference -- refs #11505
Refs #18586 -- Split custom_pk test.
Refs #18586 -- Split custom manager tests.
Readded test inadvertently removed in last commit.
Refs #18586 -- Refactored expressions tests.
Refs #20392 -- Loads fixtures once within TestCase