Update Rust crate mdbook to ^0.4.34

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
mdbook	dependencies	patch	^0.4.33 -> ^0.4.34

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Release Notes

rust-lang/mdBook (mdbook)

### [`v0.4.34`](https://togithub.com/rust-lang/mdBook/blob/HEAD/CHANGELOG.md#mdBook-0434) [Compare Source](https://togithub.com/rust-lang/mdBook/compare/v0.4.33...v0.4.34) [v0.4.33...v0.4.34](https://togithub.com/rust-lang/mdBook/compare/v0.4.33...v0.4.34) ##### Fixed - Fixed file change watcher failing on macOS with a large number of files. [#​2157](https://togithub.com/rust-lang/mdBook/pull/2157)

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