chore(deps): update dependency sphinx to v8.1.3 (#886)

This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [sphinx](https://redirect.github.com/sphinx-doc/sphinx)
([changelog](https://www.sphinx-doc.org/en/master/changes.html)) |
`==8.1.2` -> `==8.1.3` |
[![age](https://developer.mend.io/api/mc/badges/age/pypi/sphinx/8.1.3?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![adoption](https://developer.mend.io/api/mc/badges/adoption/pypi/sphinx/8.1.3?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![passing](https://developer.mend.io/api/mc/badges/compatibility/pypi/sphinx/8.1.2/8.1.3?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![confidence](https://developer.mend.io/api/mc/badges/confidence/pypi/sphinx/8.1.2/8.1.3?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|

---

### Release Notes

<details>
<summary>sphinx-doc/sphinx (sphinx)</summary>

###
[`v8.1.3`](https://redirect.github.com/sphinx-doc/sphinx/blob/HEAD/CHANGES.rst#Release-813-in-development)

[Compare
Source](https://redirect.github.com/sphinx-doc/sphinx/compare/v8.1.2...v8.1.3)

\==============================

## Bugs fixed

-
[#&#8203;13013](https://redirect.github.com/sphinx-doc/sphinx/issues/13013):
Restore support for :func:`!cut_lines` with no object type.
    Patch by Adam Turner.

</details>

---

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docs/requirements.txt

@@ -1,6 +1,6 @@
 myst-parser==4.0.0
 rstcheck==6.2.4
-sphinx==8.1.2
+sphinx==8.1.3
 nbsphinx==0.9.5
 sphinx-autobuild==2024.10.3
 sphinx-markdown-parser==0.2.4