gh-101100: Fix sphinx warnings in library/enum.rst

[sobolevn]

Before:

/Users/sobolev/Desktop/cpython2/Doc/library/enum.rst:798: WARNING: py:attr reference target not found: Enum._name_
/Users/sobolev/Desktop/cpython2/Doc/library/enum.rst:799: WARNING: py:attr reference target not found: Enum._value_
/Users/sobolev/Desktop/cpython2/Doc/library/enum.rst:805: WARNING: py:attr reference target not found: Enum._order_

It renders just fine:

I though that I can possibly define these attributes in-place, but their rendering would be very strange this way. So, I went with a little duplication.

• Issue: Fix all Sphinx reference warnings in the documentation #101100

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📚 Documentation preview 📚: https://cpython-previews--114696.org.readthedocs.build/

[hugovk]

Technically looks okay, but let's check with @ethanfurman: if the whole point of _order_ is for Python 2/3 consistency, do we need to keep that detail in the docs?

[ethanfurman]

A minor change, then good to go!

[bedevere-app]

When you're done making the requested changes, leave the comment: I have made the requested changes; please review again.

[miss-islington-app]

Thanks @sobolevn for the PR, and @hugovk for merging it 🌮🎉.. I'm working now to backport this PR to: 3.11, 3.12.
🐍🍒⛏🤖

[miss-islington-app]

Sorry, @sobolevn and @hugovk, I could not cleanly backport this to 3.12 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker 553c90ccc2f5b15be76a2bb6e38d23e58d739e2f 3.12

[miss-islington-app]

Sorry, @sobolevn and @hugovk, I could not cleanly backport this to 3.11 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker 553c90ccc2f5b15be76a2bb6e38d23e58d739e2f 3.11

[sobolevn]

I will send backports PRs later 👍

[bedevere-app]

GH-115208 is a backport of this pull request to the 3.12 branch.

[bedevere-app]

GH-115209 is a backport of this pull request to the 3.11 branch.