Two test cases have been failing on FreeBSD buildbot for a while. Let's skip the error check on FreeBSD for now.

0:27:24 load avg: 1.97 Re-running test_posix in verbose mode (matching: test_sched_getaffinity, test_sched_setaffinity)
test_sched_getaffinity (test.test_posix.PosixTester.test_sched_getaffinity) ... FAIL
test_sched_setaffinity (test.test_posix.PosixTester.test_sched_setaffinity) ... FAIL
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FAIL: test_sched_getaffinity (test.test_posix.PosixTester.test_sched_getaffinity)
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Traceback (most recent call last):
  File "/usr/home/buildbot/python/pull_request.koobs-freebsd-564d/build/Lib/test/test_posix.py", line 1197, in test_sched_getaffinity
    self.assertRaises(OSError, posix.sched_getaffinity, -1)
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: OSError not raised by sched_getaffinity
======================================================================
FAIL: test_sched_setaffinity (test.test_posix.PosixTester.test_sched_setaffinity)
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Traceback (most recent call last):
  File "/usr/home/buildbot/python/pull_request.koobs-freebsd-564d/build/Lib/test/test_posix.py", line 1215, in test_sched_setaffinity
    self.assertRaises(OSError, posix.sched_setaffinity, -1, mask)
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: OSError not raised by sched_setaffinity
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Ran 2 tests in 0.015s