Add What's New entry about Emscripten changes

[hoodmane]

---

📚 Documentation preview 📚: https://cpython-previews--137035.org.readthedocs.build/

[hoodmane]

Okay I updated it with the suggested changes. Thanks @hugovk @emmatyping @AA-Turner !

[freakboy3742]

👍

[miss-islington-app]

Thanks @hoodmane for the PR, and @AA-Turner for merging it 🌮🎉.. I'm working now to backport this PR to: 3.14.
🐍🍒⛏🤖 I'm not a witch! I'm not a witch!

[bedevere-app]

GH-137192 is a backport of this pull request to the 3.14 branch.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot AMD64 CentOS9 NoGIL Refleaks 3.x (tier-1) has failed when building commit d7e12a3.

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/1610/builds/1822) and take a look at the build logs.
4. Check if the failure is related to this commit (d7e12a3) 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/1610/builds/1822

Failed tests:

• test_site
• test_free_threading

Failed subtests:

• test_s_option - test.test_site.HelperFunctionsTests.test_s_option

Test leaking resources:

• test_free_threading: file descriptors

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.itamaro-centos-aws.refleak.nogil/build/Lib/test/test_site.py", line 259, in test_s_option
    self.assertIn(usersite, sys.path)
    ~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^
AssertionError: '/home/buildbot/.local/lib/python3.15t/site-packages' not found in ['/home/buildbot/buildarea/3.x.itamaro-centos-aws.refleak.nogil/build', '/home/buildbot/buildarea/3.x.itamaro-centos-aws.refleak.nogil/build/target/lib/python315t.zip', '/home/buildbot/buildarea/3.x.itamaro-centos-aws.refleak.nogil/build/Lib', '/home/buildbot/buildarea/3.x.itamaro-centos-aws.refleak.nogil/build/build/lib.linux-x86_64-3.15']