gh-132893: Minor edits to the statistics module PR

[rhettinger]

• The Misc/NEWS entry was inaccurate. For statistics.NormalDist.cdf, the noticeable improvement was for any x positive or negative that is below the mean.

• Eliminate a temporary variable that was only used once.

• Issue: Improve accuracy of NormalDist.cdf #132893

[AA-Turner]

Edited the PR title to stop the bot from complaining.

A

[skirpichev]

Right, this is more accurate wrt tests in the issue thread. Maybe "for inputs below the mean"?

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot s390x Fedora Stable Clang 3.x (tier-3) has failed when building commit 219b1f9.

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/1670/builds/289) and take a look at the build logs.
4. Check if the failure is related to this commit (219b1f9) 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/1670/builds/289

Failed tests:

• test_threading

Failed subtests:

• test_join_finished_daemon_thread_in_finalization - test.test_threading.ThreadTests.test_join_finished_daemon_thread_in_finalization

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

==

Click to see traceback logs

Traceback (most recent call last):
  File "/home/buildbot/buildarea/3.x.cstratak-fedora-stable-s390x.clang/build/Lib/test/test_threading.py", line 1242, in test_join_finished_daemon_thread_in_finalization
    self.assertEqual(err, b"")
    ~~~~~~~~~~~~~~~~^^^^^^^^^^
AssertionError: b'Exception ignored while calling deallocat[137 chars]: \n' != b''