gh-90756: Fix ElementTree.write XML prolog for encoding 'utf-8-sig'

[pepr]

bpo-46598: Fix ElementTree.write XML prolog for encoding 'utf-8-sig'

When ElementTree object is to be written to the file, and when BOM
is needed, the 'utf-8-sig' can be used for the purpose.
However, the XML prolog then looks like...

<?xml version='1.0' encoding='utf-8-sig'?>

... and that encoding in the prolog makes no sense. Therefore,
the utf-8-sig is changed to utf-8 for the purpose.

https://bugs.python.org/issue46598

• Issue: ElementTree: wrong XML prolog for the utf-8-sig encoding #90756

[the-knights-who-say-ni]

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@pepr

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[pepr]

Hello all,

Finally, I have found how to add my GitHub name to the b.p.o. Done. I have also signed the PSF contributor agreement.

The bpo-46598 was created, and the PR at b.p.o linked was added to point here.

The pull-request changes should be easily understandable, and I have tried it on my local computer.

Have a nice day,
Petr

[corona10]

Please add the NEW.d for behavior changing

[bedevere-bot]

A Python core developer has requested some changes be made to your pull request before we can consider merging it. If you could please address their requests along with any other requests in other reviews from core developers that would be appreciated.

Once you have made the requested changes, please leave a comment on this pull request containing the phrase I have made the requested changes; please review again. I will then notify any core developers who have left a review that you're ready for them to take another look at this pull request.

[pepr]

@corona10: Sorry, I am new in this workflow. What does it mean the "add the NEW.d for behavior changing"? Is it expected from me?

[scoder]

Thanks. You need to include a NEWS entry to describe the change.
https://devguide.python.org/committing/#updating-news-and-what-s-new-in-python

Also, this needs a test. See the ElementTree tests under Lib/test/ There are already some that deal with encodings and the XML prologue.

[github-actions]

This PR is stale because it has been open for 30 days with no activity.

[bedevere-app]

Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

If this change has little impact on Python users, wait for a maintainer to apply the skip news label instead.