gh-109276: regrtest: add WORKER_FAILED state

[vstinner]

Rename WORKER_ERROR to WORKER_BUG. Add WORKER_FAILED state: it does not stop the manager, whereas WORKER_BUG does.

Change also TestResults.display_result() order: display failed tests at the end, the important important information.

• Issue: Enhance Python regrtest test runner (test.libregrtest) #109276

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot AMD64 FreeBSD 3.x has failed when building commit 2c23419.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/all/#builders/1223/builds/292) and take a look at the build logs.
4. Check if the failure is related to this commit (2c23419) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/all/#builders/1223/builds/292

Failed tests:

• test.test_concurrent_futures.test_process_pool

Summary of the results of the build (if available):

==

Click to see traceback logs

Traceback (most recent call last):
  File "/buildbot/buildarea/3.x.ware-freebsd/build/Lib/multiprocessing/forkserver.py", line 274, in main
    code = _serve_one(child_r, fds,
           ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/buildbot/buildarea/3.x.ware-freebsd/build/Lib/multiprocessing/forkserver.py", line 313, in _serve_one
    code = spawn._main(child_r, parent_sentinel)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/buildbot/buildarea/3.x.ware-freebsd/build/Lib/multiprocessing/spawn.py", line 132, in _main
    self = reduction.pickle.load(from_parent)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/buildbot/buildarea/3.x.ware-freebsd/build/Lib/multiprocessing/synchronize.py", line 115, in __setstate__
    self._semlock = _multiprocessing.SemLock._rebuild(*state)
                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
FileNotFoundError: [Errno 2] No such file or directory
Traceback (most recent call last):
  File "/buildbot/buildarea/3.x.ware-freebsd/build/Lib/multiprocessing/forkserver.py", line 274, in main
    code = _serve_one(child_r, fds,
           ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/buildbot/buildarea/3.x.ware-freebsd/build/Lib/multiprocessing/forkserver.py", line 313, in _serve_one
    code = spawn._main(child_r, parent_sentinel)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/buildbot/buildarea/3.x.ware-freebsd/build/Lib/multiprocessing/spawn.py", line 132, in _main
    self = reduction.pickle.load(from_parent)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/buildbot/buildarea/3.x.ware-freebsd/build/Lib/multiprocessing/synchronize.py", line 115, in __setstate__
    self._semlock = _multiprocessing.SemLock._rebuild(*state)
                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
FileNotFoundError: [Errno 2] No such file or directory
Timeout (0:20:00)!
Thread 0x0000000830bca000 (most recent call first):
  File "/buildbot/buildarea/3.x.ware-freebsd/build/Lib/threading.py", line 348 in wait
  File "/buildbot/buildarea/3.x.ware-freebsd/build/Lib/multiprocessing/queues.py", line 251 in _feed
  File "/buildbot/buildarea/3.x.ware-freebsd/build/Lib/threading.py", line 1003 in run
  File "/buildbot/buildarea/3.x.ware-freebsd/build/Lib/threading.py", line 1066 in _bootstrap_inner
  File "/buildbot/buildarea/3.x.ware-freebsd/build/Lib/threading.py", line 1023 in _bootstrap