* Revert "Reverted "Fixed #33213 -- Doc'd testing code coverage in parallel and used it.""
This reverts commit 78da5ca0c1.
* Restored coverage multiprocess concurrency with threads
Investigating https://github.com/nedbat/coveragepy/issues/1585 revealed
that thread tracing gets disabled when passing
`concurrency = multiprocessing`. Adding `thread` restores it, and
ensures that the `auser()` is reported as covered since the test suite
uses `AsyncToSync` to execute this middleware (which spawns threads).
Thanks to Preston Timmons for the bulk of the work on the patch, especially
updating Django's own test suite to comply with the requirements of the new
runner. Thanks also to Jannis Leidel and Mahdi Yusuf for earlier work on the
patch and the discovery runner.
Refs #11077, #17032, and #18670.
