chore(deps): update dependency pymdown-extensions to v10.21.2 (#2281)

This PR contains the following updates:

| Package | Change |
[Age](https://docs.renovatebot.com/merge-confidence/) |
[Confidence](https://docs.renovatebot.com/merge-confidence/) |
|---|---|---|---|
|
[pymdown-extensions](https://redirect.github.com/facelessuser/pymdown-extensions)
| `==10.21` → `==10.21.2` |
![age](https://developer.mend.io/api/mc/badges/age/pypi/pymdown-extensions/10.21.2?slim=true)
|
![confidence](https://developer.mend.io/api/mc/badges/confidence/pypi/pymdown-extensions/10.21/10.21.2?slim=true)
|

---

> [!WARNING]
> Some dependencies could not be looked up. Check the [Dependency
Dashboard](../issues/355) for more information.

---

### Release Notes

<details>
<summary>facelessuser/pymdown-extensions (pymdown-extensions)</summary>

###
[`v10.21.2`](https://redirect.github.com/facelessuser/pymdown-extensions/releases/tag/10.21.2):
10.21. 2

[Compare
Source](https://redirect.github.com/facelessuser/pymdown-extensions/compare/10.21...10.21.2)

#### 10.21.2

- **FIX**: Highlight: Latest Pygments versions cannot handle a
"filename" for code block titles of `None`.

</details>

---

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docs/requirements.txt

@@ -2,4 +2,4 @@ mkdocs==1.6.1
 mkdocs-material==9.7.6
 mkdocs-material-extensions==1.3.1
 mkdocs-video==1.5.0
-pymdown-extensions==10.21
+pymdown-extensions==10.21.2