gh-143602: Fix duplicate buffer exports in io.BytesIO.write

[superboy-zjc]

Fix a inconsistency issue in io.BytesIO.write() where the buffer was exported twice, which could lead to unexpected data overwrites and position drift when the buffer changes between exports.

• Issue: Incorrect behavior of BytesIO.write() when the size of the written data changed during writing #143602

[vstinner]

LGTM. The NEWS entry can be enhanced, but I cannot propose a better description.

[miss-islington-app]

Thanks @superboy-zjc for the PR, and @vstinner for merging it 🌮🎉.. I'm working now to backport this PR to: 3.14.
🐍🍒⛏🤖

[miss-islington-app]

Thanks @superboy-zjc for the PR, and @vstinner for merging it 🌮🎉.. I'm working now to backport this PR to: 3.13.
🐍🍒⛏🤖 I'm not a witch! I'm not a witch!

[miss-islington-app]

Sorry, @superboy-zjc and @vstinner, I could not cleanly backport this to 3.13 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker c461aa99e2fabbaf5859c0a8a93e08306ee8115d 3.13

[miss-islington-app]

Sorry, @superboy-zjc and @vstinner, I could not cleanly backport this to 3.14 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker c461aa99e2fabbaf5859c0a8a93e08306ee8115d 3.14

[bedevere-app]

GH-143872 is a backport of this pull request to the 3.14 branch.

[vstinner]

I backported the change to 3.14: #143872.

[vstinner]

Merged, thanks for your contribution @superboy-zjc.

[serhiy-storchaka]

LGTM. 👍

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot ARM64 macOS 3.14 (tier-2) has failed when building commit 1241432.

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/1772/builds/811) and take a look at the build logs.
4. Check if the failure is related to this commit (1241432) 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/1772/builds/811

Failed tests:

• test_urllib2net

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

==

Click to see traceback logs

remote: Enumerating objects: 11, done.        
remote: Counting objects:  25% (1/4)        
remote: Counting objects:  50% (2/4)        
remote: Counting objects:  75% (3/4)        
remote: Counting objects: 100% (4/4)        
remote: Counting objects: 100% (4/4), done.        
remote: Compressing objects:  33% (1/3)        
remote: Compressing objects:  66% (2/3)        
remote: Compressing objects: 100% (3/3)        
remote: Compressing objects: 100% (3/3), done.        
remote: Total 11 (delta 1), reused 1 (delta 1), pack-reused 7 (from 2)        
From https://github.com/python/cpython
 * branch                    3.14       -> FETCH_HEAD
Note: switching to '1241432150f6342e3d38c5a80a19c8c157a4ebe8'.

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Turn off this advice by setting config variable advice.detachedHead to false

HEAD is now at 1241432150f [3.14] gh-143602: Fix duplicate buffer exports in io.BytesIO.write (#143629) (#143872)
Switched to and reset branch '3.14'

make: *** [buildbottest] Error 2