chore(deps): update dependency sphinx to v8.1.2 (#883)

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)) |
`==8.1.1` -> `==8.1.2` |
[![age](https://developer.mend.io/api/mc/badges/age/pypi/sphinx/8.1.2?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![adoption](https://developer.mend.io/api/mc/badges/adoption/pypi/sphinx/8.1.2?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![passing](https://developer.mend.io/api/mc/badges/compatibility/pypi/sphinx/8.1.1/8.1.2?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![confidence](https://developer.mend.io/api/mc/badges/confidence/pypi/sphinx/8.1.1/8.1.2?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|

---

### Release Notes

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

###
[`v8.1.2`](https://redirect.github.com/sphinx-doc/sphinx/blob/HEAD/CHANGES.rst#Release-812-in-development)

[Compare
Source](https://redirect.github.com/sphinx-doc/sphinx/compare/v8.1.1...v8.1.2)

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

## Bugs fixed

-
[#&#8203;13012](https://redirect.github.com/sphinx-doc/sphinx/issues/13012):
Expose :exc:`sphinx.errors.ExtensionError` in `sphinx.util`
    for backwards compatibility.
    This will be removed in Sphinx 9, as exposing the exception
    in `sphinx.util` was never intentional.
:exc:`!ExtensionError` has been part of `sphinx.errors` since Sphinx
0.9.
    Patch by Adam Turner.

</details>

---

### Configuration

📅 **Schedule**: Branch creation - At any time (no schedule defined),
Automerge - At any time (no schedule defined).

🚦 **Automerge**: Disabled by config. Please merge this manually once you
are satisfied.

♻ **Rebasing**: Whenever PR becomes conflicted, or you tick the
rebase/retry checkbox.

🔕 **Ignore**: Close this PR and you won't be reminded about this update
again.

---

- [ ] <!-- rebase-check -->If you want to rebase/retry this PR, check
this box

---

This PR was generated by [Mend Renovate](https://mend.io/renovate/).
View the [repository job
log](https://developer.mend.io/github/secretflow/spu).

<!--renovate-debug:eyJjcmVhdGVkSW5WZXIiOiIzOC4xMTUuMSIsInVwZGF0ZWRJblZlciI6IjM4LjExNS4xIiwidGFyZ2V0QnJhbmNoIjoibWFpbiIsImxhYmVscyI6WyJkZXBlbmRlbmNpZXMiXX0=-->

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

docs/requirements.txt

@@ -1,6 +1,6 @@
 myst-parser==4.0.0
 rstcheck==6.2.4
-sphinx==8.1.1
+sphinx==8.1.2
 nbsphinx==0.9.5
 sphinx-autobuild==2024.10.3
 sphinx-markdown-parser==0.2.4