chore(deps): update dependency mkdocs-material to v9.6.21 (#2328)

This PR contains the following updates:

| Package | Change | Age | Confidence |
|---|---|---|---|
|
[mkdocs-material](https://redirect.github.com/squidfunk/mkdocs-material)
([changelog](https://squidfunk.github.io/mkdocs-material/changelog/)) |
`==9.6.20` -> `==9.6.21` |
[![age](https://developer.mend.io/api/mc/badges/age/pypi/mkdocs-material/9.6.21?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|
[![confidence](https://developer.mend.io/api/mc/badges/confidence/pypi/mkdocs-material/9.6.20/9.6.21?slim=true)](https://docs.renovatebot.com/merge-confidence/)
|

---

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

---

### Release Notes

<details>
<summary>squidfunk/mkdocs-material (mkdocs-material)</summary>

###
[`v9.6.21`](https://redirect.github.com/squidfunk/mkdocs-material/releases/tag/9.6.21):
mkdocs-material-9.6.21

[Compare
Source](https://redirect.github.com/squidfunk/mkdocs-material/compare/9.6.20...9.6.21)

- Updated Serbian translations
- Fixed
[#&#8203;8458](https://redirect.github.com/squidfunk/mkdocs-material/issues/8458):
Temporary pin of click dependency

</details>

---

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Author: slack-oss-bot

.github/workflows/mkdocs-requirements.txt

@@ -7,7 +7,7 @@ Markdown==3.9
 MarkupSafe==3.0.3
 mkdocs==1.6.1
 mkdocs-macros-plugin==1.4.0
-mkdocs-material==9.6.20
+mkdocs-material==9.6.21
 mkdocs-material-extensions==1.3.1
 Pygments==2.19.2
 pymdown-extensions==10.16.1