Tests: Don't measure CI performance in tests, don't test maximum elapsed time

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A test should not measure a CI performance: don't test maximum elapsed time.

Linked PRs

• gh-110666: Fix multiprocessing test_terminate() elapsed #110667
• [3.12] gh-110666: Fix multiprocessing test_terminate() elapsed (GH-110667) #110668
• [3.11] gh-110666: Fix multiprocessing test_terminate() elapsed (GH-110667) #110669

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Example: fail on GHA Windows x86: https://github.com/python/cpython/actions/runs/6476324922/job/17584898557?pr=110663

FAIL: test_terminate (test.test_multiprocessing_spawn.test_threads.WithThreadsTestPool.test_terminate)
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Traceback (most recent call last):
  File "D:\a\cpython\cpython\Lib\test\_test_multiprocessing.py", line 2688, in test_terminate
    self.assertLess(join.elapsed, 2.0)
AssertionError: 27.2650000000001 not less than 2.0

On the same PR, the same test failed on GHA macOS and GHA Ubuntu jobs.