Refs #19716.

Refs #14334

Thanks inglesp for the report.

Thanks CHI Cheng for the report.

Thanks Corey Farwell for the report and Tim Graham for the review.
Thanks also to Inada Naoki for creating and maintaining mysqlclient.

Thanks Bjarkias for the report.

Basically a4737bf6 reapplied.

Thanks gavinwahl for the report.

In some test combinations, having contrib.auth available but not
contrib.contenttypes can produce failures while creating permissions.

Thanks Keryn Knight for the report.

Thanks Naddiseo for the report, Andrew Godwin for guidance,
and Shai Berger for review.

That test might not always execute, but can be executed when the
parent test label is explicitely given.

Thanks dfunckt and Tim Graham.

Previously a RuntimeError was raised every time two models clashed
in the app registry. This prevented reloading a module in a REPL;
while it's not recommended to do so, we decided not to forbid this
use-case by turning the error into a warning.

Thanks @dfunckt and Sergey Pashinin for the initial patches.

Thanks prathik for the report.

This includes the following improvements:

- The type of the style object is now called 'Style' rather than 'dummy'.
- The new make_style() function allows generating a Style object directly
  from a config string. Before the only way to get a style object was
  through the environ and it also required that the terminal supported
  colors which isn't necessarily the case when testing.
- The output of no_style() is now cached with @lru_cache.
- The output of no_style() now has the same set of attributes as the
  other Style objects. Previously it allowed anything to pass through
  with __getattr__.

Thanks Tim Graham for the review.

This is a leftover from 5612f54b.