gh-57491: Reduce the EPUB table of contents depth to 2

[Danishk2445]

Set epub_tocdepth = 2 in Doc/conf.py, as @m-aciek suggested in the issue.

With Sphinx's default depth of 3, the EPUB table of contents has 1,516 entries. 1,328 of them are third-level, including every section of every "What's New" document. With depth 2 it has 188 entries. Every "What's New" version and every standard library category is still listed, and the pages under them are one step away through each chapter's own contents.

Tested with make -C Doc epub: the build passes with --fail-on-warning, and epubcheck plus Doc/tools/check-epub.py report no new errors. Since this is only a config change, it may be worth backporting, as @merwok suggested.

• Issue: the table of contents in epub file is too long #57491

[python-cla-bot]

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[read-the-docs-community]

Documentation build overview

📚 cpython-previews | 🛠️ Build #34741034 | 📁 Comparing 1f45dc0 against main (0b72907)

  🔍 Preview build  

1 file changed

± whatsnew/changelog.html

[m-aciek]

This looks good to me, thank you! Could you attach a screenshot for before/after changes for a first (two?) page(s) of table of contents?

[StanFromIreland]

Seems fine to me too, but yes, please share some screenshots.

[Danishk2445]

Thanks for the reviews. Here are the before and after screenshots of the first two pages of the table of contents:

[miss-islington-app]

Thanks @Danishk2445 for the PR, and @hugovk for merging it 🌮🎉.. I'm working now to backport this PR to: 3.13, 3.14, 3.15.
🐍🍒⛏🤖

[bedevere-app]

GH-158249 is a backport of this pull request to the 3.15 branch.

[bedevere-app]

GH-158250 is a backport of this pull request to the 3.14 branch.

[bedevere-app]

GH-158251 is a backport of this pull request to the 3.13 branch.