Corrected deprecation warnings for RedirectView; refs #21587.
Fixed #23423 -- Added unaccent lookup in django.contrib.postgres
Silenced all admin validation warnings.

Warnings could escape depending on the order in which tests were run.
Removed instructions to create a PostgreSQL cluster in GIS docs

Creating a new cluster is neither required not recommendable for
most users. The previous section explains how to create a user
with sufficient permissions to automatically create a database
during tests.
Fixed #23923 -- Promoted Django's deprecation warnings to errors in runtests.py
Fixed #17890 -- Added an extra_context parameter to AdminSite.password_change().
Fixed #23930 -- Added copies of captured_std* managers from CPython's test.support.

StringIO import was adapted for compatibility with Python 2.
Fixed #23933 -- Made override_settings(DATABASE_ROUTERS) affect the master router.
Replaced router.routers usage with override_settings(DATABASE_ROUTERS).
Corrected a docstring in tests/migrations/test_operations.py.
Removed a no-op statement in tests/multiple_database/tests.py.
Removed an incorrect docstring in tests/multiple_database/tests.py.
Removed a clear_cache statement in contrib.sites.create_default_site.

Refs: #7514, #23929.
Fixed #23929 -- Added more tests for create_default_site.

Refs: #15346, #15573, #16353, #16828.