Remove text-mangling of default values.
Fixed #23961 -- Clarified when makemigrations will create a directory.
Refs #23947 -- Prevented staticfiles tests from having side effects.
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.
Fixed #23674 -- Fixed a crash when a MultiValueField has invalid data.
Refs #20392 -- Load fixtures once within TestCase
Fixed template tag braces spacing.
Fixed #23941 -- Removed implicit decimal formatting from expressions.
Fixed #23857 -- Fixed admin crash with "save as new" and deleting inline.

Thanks amarandon for the report.
Fixed postgis test database initialization

Refs #20968. Allow querying template_postgis presence without
existing test database.