docs: fallback for restoring right scroll menu

[Borda]

What does this PR do?

actual state

after fallback

Before submitting

• Was this discussed/agreed via a GitHub issue? (not for typos and docs)
• Did you read the contributor guideline, Pull Request section?
• Did you make sure your PR does only one thing, instead of bundling different changes together?
• Did you make sure to update the documentation with your changes? (if necessary)
• Did you write any new necessary tests? (not for typos and docs)
• Did you verify new and existing tests pass locally with your changes?
• Did you list all the breaking changes introduced by this pull request?
• Did you update the CHANGELOG? (not for typos, docs, test updates, or minor internal changes/refactors)

PR review

Anyone in the community is welcome to review the PR.
Before you start reviewing, make sure you have read the review guidelines. In short, see the following bullet-list:

Reviewer checklist

• Is this pull request ready for review? (if not, please submit in draft mode)
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cc @Borda @carmocca @justusschock @awaelchli

[github-actions]

⚡ Required checks status: All passing 🟢

Groups summary

🟢 fabric: Docs

Check ID	Status
make-doctest (fabric)	success	✅
make-html (fabric)	success	✅

These checks are required after the changes to docs/source-fabric/conf.py, requirements/docs.txt.

🟢 pytorch_lightning: Docs

Check ID	Status
make-doctest (pytorch)	success	✅
make-html (pytorch)	success	✅

These checks are required after the changes to docs/source-pytorch/conf.py, requirements/docs.txt.

🟢 lightning_app: Docs

Check ID	Status
make-doctest (app)	success	✅
make-html (app)	success	✅

These checks are required after the changes to docs/source-app/conf.py, requirements/docs.txt.

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Thank you for your contribution! 💜

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