Tkinter: `test_boundary_values_accepted` fails

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Bug report

Bug description:

test.test_tkinter.test_simpledialog.QueryDialogTest.test_boundary_values_accepted is failing, for example in this run https://github.com/python/cpython/actions/runs/29705949750/job/88242885156?pr=154202:

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FAIL: test_boundary_values_accepted (test.test_tkinter.test_simpledialog.QueryDialogTest.test_boundary_values_accepted)
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Traceback (most recent call last):
 File "D:\a\cpython\cpython\Lib\test\test_tkinter\test_simpledialog.py", line 246, in test_boundary_values_accepted
 self.assertEqual(d.result, 10)
 ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^
AssertionError: None != 10

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I can also reproduce the failure locally on the main branch:

======================================================================
FAIL: test_boundary_values_accepted (test.test_tkinter.test_simpledialog.QueryDialogTest.test_boundary_values_accepted)
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Traceback (most recent call last):
 File "/home/a/cpython/Lib/test/test_tkinter/test_simpledialog.py", line 536, in test_boundary_values_accepted
 self.assertEqual(d.result, 20)
 ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^
AssertionError: None != 20

======================================================================

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux, Windows

Linked PRs

• gh-154357: Fix race condition in test_simpledialog by explicitly setting focus to entry #154368
• gh-154357: Hide the root window in the tkinter dialog tests #154370

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This test was added in #151856.

Cc @serhiy-storchaka