gh-139927: Fix test_embed on OpenIndiana

[vstinner]

Avoid swprintf() function in Programs/_testembed.c since it doesn't work as expected on OpenIndiana.

• Issue: test_init_use_frozen_modules fails on OpenIndiana #139927

[vstinner]

cc @mtelka

[miss-islington-app]

Thanks @vstinner for the PR 🌮🎉.. I'm working now to backport this PR to: 3.13, 3.14.
🐍🍒⛏🤖

[bedevere-app]

GH-142520 is a backport of this pull request to the 3.14 branch.

[bedevere-app]

GH-142521 is a backport of this pull request to the 3.13 branch.

[mtelka]

I can confirm that Python 3.14.2 + this change succeeds to run the test_embed test. Thank you!

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot AMD64 Windows11 Refleaks 3.13 (tier-1) has failed when building commit 2b0ccce.

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/#/builders/1484/builds/896) and take a look at the build logs.
4. Check if the failure is related to this commit (2b0ccce) 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/#/builders/1484/builds/896

Failed tests:

• test_io

Failed subtests:

• test_daemon_threads_shutdown_stdout_deadlock - test.test_io.CMiscIOTest.test_daemon_threads_shutdown_stdout_deadlock

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

==

Click to see traceback logs

Traceback (most recent call last):
  File "b:\uildarea\3.13.ware-win11.refleak\build\Lib\test\test_io.py", line 4734, in test_daemon_threads_shutdown_stdout_deadlock
    self.check_daemon_threads_shutdown_deadlock('stdout')
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^
  File "b:\uildarea\3.13.ware-win11.refleak\build\Lib\test\test_io.py", line 4727, in check_daemon_threads_shutdown_deadlock
    self.assertRegex(err, pattern)
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^
AssertionError: Regex didn't match: "Fatal Python error: _enter_buffered_busy: could not acquire lock for <(_io\\.)?BufferedWriter name='<stdout>'> at interpreter shutdown, possibly due to daemon threads" not found in ''