Update Rust crate mdbook to v0.4.42 (#20629)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [mdbook](https://redirect.github.com/rust-lang/mdBook) | dependencies
| patch | `0.4.40` -> `0.4.42` |

---

### Release Notes

<details>
<summary>rust-lang/mdBook (mdbook)</summary>

###
[`v0.4.42`](https://redirect.github.com/rust-lang/mdBook/blob/HEAD/CHANGELOG.md#mdBook-0442)

[Compare
Source](https://redirect.github.com/rust-lang/mdBook/compare/v0.4.41...v0.4.42)


[v0.4.41...v0.4.42](https://redirect.github.com/rust-lang/mdBook/compare/v0.4.41...v0.4.42)

##### Fixed

-   Fixed chapter list folding.
[#&#8203;2473](https://redirect.github.com/rust-lang/mdBook/pull/2473)

###
[`v0.4.41`](https://redirect.github.com/rust-lang/mdBook/blob/HEAD/CHANGELOG.md#mdBook-0441)

[Compare
Source](https://redirect.github.com/rust-lang/mdBook/compare/v0.4.40...v0.4.41)


[v0.4.40...v0.4.41](https://redirect.github.com/rust-lang/mdBook/compare/v0.4.40...v0.4.41)

**Note:** If you have a custom `index.hbs` theme file, you will need to
update it to the latest version.

##### Added

-   Added preliminary support for Rust 2024 edition.
[#&#8203;2398](https://redirect.github.com/rust-lang/mdBook/pull/2398)
-   Added a full example of the remove-emphasis preprocessor.
[#&#8203;2464](https://redirect.github.com/rust-lang/mdBook/pull/2464)

##### Changed

-   Adjusted styling of clipboard/play icons.
[#&#8203;2421](https://redirect.github.com/rust-lang/mdBook/pull/2421)
-   Updated to handlebars v6.
[#&#8203;2416](https://redirect.github.com/rust-lang/mdBook/pull/2416)
-   Attr and section rules now have specific code highlighting.
[#&#8203;2448](https://redirect.github.com/rust-lang/mdBook/pull/2448)
- The sidebar is now loaded from a common file, significantly reducing
the book size when there are many chapters.
[#&#8203;2414](https://redirect.github.com/rust-lang/mdBook/pull/2414)
-   Updated dependencies.
[#&#8203;2470](https://redirect.github.com/rust-lang/mdBook/pull/2470)

##### Fixed

-   Improved theme support when JavaScript is disabled.
[#&#8203;2454](https://redirect.github.com/rust-lang/mdBook/pull/2454)
-   Fixed broken themes when localStorage has an invalid theme id.
[#&#8203;2463](https://redirect.github.com/rust-lang/mdBook/pull/2463)
- Adjusted the line-height of superscripts (and footnotes) to avoid
adding extra space between lines.
[#&#8203;2465](https://redirect.github.com/rust-lang/mdBook/pull/2465)

</details>

---

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