[3.12] gh-103186: Fix or catch 'extra' stderr output from unittests (GH-103196) ...

[3.12] gh-103186: Fix or catch 'extra' stderr output from unittests (GH-103196) (#106605)

gh-103186: Fix or catch 'extra' stderr output from unittests (GH-103196)

Reduce test noise by fixing or catching and testing stderr messages from individual tests.

test_cmd_line_script.test_script_as_dev_fd calls spawn_python and hence subprocess.Popen with incompatible arguments. On POSIX, pass_fds forces close_fds to be True (subprocess.py line 848). Correct the call.

test_uuid.test_cli_namespace_required_for_uuid3: when the namespace is omitted, uuid.main calls argparse.Argument_Parser.error, which prints to stderr before calling sys.exit, which raises SystemExit. Unittest assertRaises catches the exception but not the previous output. Catch the output and test it.

test_warnings.test_catchwarnings_with_simplefilter_error similarly prints before raising. Catch the output and test it.
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(cherry picked from commit 9d582250d8fde240b8e7299b74ba888c574f74a3)

Co-authored-by: Ijtaba Hussain <ijtabahussain@live.com>
Co-authored-by: Oleg Iarygin <oleg@arhadthedev.net>