[3.11] gh-109832: concurrent.futures test_deadlock restores sys.stderr (GH-109887) (#109893)

gh-109832: concurrent.futures test_deadlock restores sys.stderr (GH-109887)

test_error_at_task_unpickle() and
test_error_during_result_unpickle_in_result_handler() now restore
sys.stderr which is overriden by _raise_error_ignore_stderr().
(cherry picked from commit 2897142d2ec0930a8991af964c798b68fb6dcadd)

Co-authored-by: Victor Stinner <vstinner@python.org>