test_signal fails in AMD64 Debian PGO 3.x:

== Tests result: FAILURE then FAILURE ==
406 tests OK.
10 slowest tests:
- test_concurrent_futures: 2 min 37 sec
- test_multiprocessing_spawn: 2 min 3 sec
- test_multiprocessing_forkserver: 1 min 28 sec
- test_multiprocessing_fork: 1 min 17 sec
- test_gdb: 46 sec 874 ms
- test_asyncio: 46 sec 166 ms
- test_tools: 37 sec 582 ms
- test_io: 35 sec 518 ms
- test_tokenize: 34 sec 631 ms
- test_subprocess: 34 sec 302 ms
1 test failed:
    test_signal
13 tests skipped:
    test_devpoll test_ioctl test_kqueue test_msilib test_ossaudiodev
    test_startfile test_tix test_tk test_ttk_guionly test_winconsoleio
    test_winreg test_winsound test_zipfile64

https://buildbot.python.org/all/#/builders/47/builds/2251/steps/4/logs/stdio

test_valid_signals (test.test_signal.WindowsSignalTests) ... skipped 'Windows specific'
======================================================================
FAIL: test_keyboard_interrupt_communicated_to_shell (test.test_signal.PosixTests)
KeyboardInterrupt exits such that shells detect a ^C.
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Traceback (most recent call last):
  File "/var/lib/buildbot/slaves/enable-optimizations-bot/3.x.gps-debian-profile-opt.nondebug/build/Lib/test/test_signal.py", line 121, in test_keyboard_interrupt_communicated_to_shell
    self.assertNotIn(b"TESTFAIL", process.stdout)
AssertionError: b'TESTFAIL' unexpectedly found in b'TESTFAIL using bash 4.4.12(1)-release\n'
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This may be related to PR11862