gh-95672: Update memory_watchdog to use test.support.get_pagesize

[hyeongyun0916]

The parts of the test(memory_watchdog) that require pagesize are integrated to use the function in support.

#102163 (comment)

• Issue: pipe test failures on some Linux configurations  #95672

[corona10]

lgtm!

[corona10]

@hyeongyun0916 nit Please care about the PR title to summarize your change.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot ARM64 macOS 3.x has failed when building commit 6059743.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/all/#builders/725/builds/3837) and take a look at the build logs.
4. Check if the failure is related to this commit (6059743) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/all/#builders/725/builds/3837

Failed tests:

• test_asyncio

Failed subtests:

• test_wait_for_race_condition - test.test_asyncio.test_waitfor.AsyncioWaitForTest.test_wait_for_race_condition

Summary of the results of the build (if available):

== Tests result: FAILURE then FAILURE ==

405 tests OK.

10 slowest tests:

• test_signal: 4 min 20 sec
• test_concurrent_futures: 2 min 33 sec
• test_multiprocessing_spawn: 2 min 10 sec
• test_ssl: 1 min 45 sec
• test_multiprocessing_forkserver: 1 min 35 sec
• test_asyncio: 1 min 29 sec
• test_math: 1 min 6 sec
• test_logging: 1 min 5 sec
• test_capi: 49.9 sec
• test_io: 39.3 sec

1 test failed:
test_asyncio

25 tests skipped:
test_check_c_globals test_devpoll test_epoll test_gdb test_idle
test_ioctl test_launcher test_msilib test_multiprocessing_fork
test_ossaudiodev test_peg_generator test_perf_profiler test_spwd
test_startfile test_tcl test_tix test_tkinter test_ttk
test_ttk_textonly test_turtle test_winconsoleio test_winreg
test_winsound test_wmi test_zipfile64

1 re-run test:
test_asyncio

Total duration: 8 min 47 sec

Click to see traceback logs

Traceback (most recent call last):
  File "/Users/buildbot/buildarea/3.x.pablogsal-macos-m1.macos-with-brew/build/Lib/asyncio/tasks.py", line 478, in wait_for
    return await fut
           ^^^^^^^^^
asyncio.exceptions.CancelledError


Traceback (most recent call last):
  File "/Users/buildbot/buildarea/3.x.pablogsal-macos-m1.macos-with-brew/build/Lib/unittest/async_case.py", line 90, in _callTestMethod
    if self._callMaybeAsync(method) is not None:
       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/buildbot/buildarea/3.x.pablogsal-macos-m1.macos-with-brew/build/Lib/unittest/async_case.py", line 112, in _callMaybeAsync
    return self._asyncioRunner.run(
           ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/buildbot/buildarea/3.x.pablogsal-macos-m1.macos-with-brew/build/Lib/asyncio/runners.py", line 118, in run
    return self._loop.run_until_complete(task)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/buildbot/buildarea/3.x.pablogsal-macos-m1.macos-with-brew/build/Lib/asyncio/base_events.py", line 664, in run_until_complete
    return future.result()
           ^^^^^^^^^^^^^^^
  File "/Users/buildbot/buildarea/3.x.pablogsal-macos-m1.macos-with-brew/build/Lib/test/test_asyncio/test_waitfor.py", line 163, in test_wait_for_race_condition
    res = await task
          ^^^^^^^^^^
  File "/Users/buildbot/buildarea/3.x.pablogsal-macos-m1.macos-with-brew/build/Lib/asyncio/tasks.py", line 477, in wait_for
    async with timeouts.timeout(timeout):
  File "/Users/buildbot/buildarea/3.x.pablogsal-macos-m1.macos-with-brew/build/Lib/asyncio/timeouts.py", line 98, in __aexit__
    raise TimeoutError
TimeoutError