Update dependency mkdocs-material to v9.5.15 (#1303)

This PR contains the following updates:

| Package | Update | Change |
|---|---|---|
| [mkdocs-material](https://github.com/squidfunk/mkdocs-material) |
patch | `==9.5.14` -> `==9.5.15` |

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### Release Notes

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

###
[`v9.5.15`](https://github.com/squidfunk/mkdocs-material/releases/tag/9.5.15):
mkdocs-material-9.5.15

[Compare
Source](https://github.com/squidfunk/mkdocs-material/compare/9.5.14...9.5.15)

-   Reverted fix for transparent iframes (9.5.14)
- Fixed
[#&#8203;6929](https://github.com/squidfunk/mkdocs-material/issues/6929):
Interference of social plugin and auto dark mode
- Fixed
[#&#8203;6938](https://github.com/squidfunk/mkdocs-material/issues/6938):
Giscus shows dark background in light mode (9.5.14 regression)

</details>

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.github/workflows/mkdocs-requirements.txt

@@ -7,7 +7,7 @@ Markdown==3.6
 MarkupSafe==2.1.5
 mkdocs==1.5.3
 mkdocs-macros-plugin==1.0.5
-mkdocs-material==9.5.14
+mkdocs-material==9.5.15
 mkdocs-material-extensions==1.3.1
 Pygments==2.17.2
 pymdown-extensions==10.7.1