Update Rust crate mdbook to ^0.4.23

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
mdbook	dependencies	patch	^0.4.22 -> ^0.4.23

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Release Notes

rust-lang/mdBook

### [`v0.4.23`](https://togithub.com/rust-lang/mdBook/blob/HEAD/CHANGELOG.md#mdBook-0423) [Compare Source](https://togithub.com/rust-lang/mdBook/compare/v0.4.22...v0.4.23) [678b469...68a75da](https://togithub.com/rust-lang/mdBook/compare/678b469...68a75da) ##### Changed - Updated all dependencies [#​1951](https://togithub.com/rust-lang/mdBook/pull/1951) [#​1952](https://togithub.com/rust-lang/mdBook/pull/1952) [#​1844](https://togithub.com/rust-lang/mdBook/pull/1844) - Updated minimum Rust version to 1.60. [#​1951](https://togithub.com/rust-lang/mdBook/pull/1951) ##### Fixed - Fixed a regression where playground code was missing hidden lines, preventing it from compiling correctly. [#​1950](https://togithub.com/rust-lang/mdBook/pull/1950)

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