Docs HTML: Remove self-closing tags

[hugovk]

Self-closing tags (<tag />) do not exist in HTML.

If a trailing / (slash) character is present in the start tag of an HTML element, HTML parsers ignore that slash character. This is especially important to remember for elements such as <script> or <ul> that do require a closing tag. In these cases, adding a trailing slash in the start tag does not close the element. Instead, the trailing slash is ignored, and the element is treated as open until an explicit closing tag is encountered or until the parser implicitly closes the element based on the HTML structure and parsing rules. For example, in the case of <div/>Some text, browsers interpret this as <div>Some text</div>, treating the slash as ignored and considering the div element to encapsulate the text that follows.

https://developer.mozilla.org/en-US/docs/Glossary/Void_element#self-closing_tags

Let's omit them: they're ignored, could be misleading (give the false impression they do something when they do not) and are ugly (IMO).

---

📚 Documentation preview 📚: https://cpython-previews--132220.org.readthedocs.build/

[picnixz]

I think we have self-closing tags in Sphinx' writers so we should also fix this upstream.

[miss-islington-app]

Thanks @hugovk for the PR 🌮🎉.. I'm working now to backport this PR to: 3.12, 3.13.
🐍🍒⛏🤖

[miss-islington-app]

Sorry, @hugovk, I could not cleanly backport this to 3.13 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker ce724571b35f4e79fff1c862fcd9afa4c26b605f 3.13

[miss-islington-app]

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

cherry_picker ce724571b35f4e79fff1c862fcd9afa4c26b605f 3.12

[bedevere-app]

GH-132228 is a backport of this pull request to the 3.13 branch.

[bedevere-app]

GH-132229 is a backport of this pull request to the 3.12 branch.