build(deps): Update Rust crate mdbook to v0.4.38

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
mdbook	dependencies	patch	0.4.37 -> 0.4.38

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Release Notes

rust-lang/mdBook (mdbook)

v0.4.38

Compare Source

v0.4.37...v0.4.38

Added

• Added nix to the default set of languages supported for syntax highlighting.
  #​2262

Changed

• The output.html.curly-quotes option has been renamed to output.html.smart-punctuation to better reflect what it does. The old option curly-quotes is kept for compatibility, but may be removed in the future.
  #​2327
• The file-watcher used in mdbook serve and mdbook watch now uses a poll-based watcher instead of the native operating system notifications. This should fix issues on various systems and environments, and more accurately detect when files change. The native watcher can still be used with the --watcher native CLI option.
  #​2325
• mdbook test output now includes color, and shows relative paths to the source.
  #​2259
• Updated dependencies, MSRV raised to 1.74
  #​2350
  #​2351
  #​2378
  #​2381

Fixed

• Reduced memory allocation when copying files.
  #​2355
• Fixed the horizontal divider in SUMMARY.md from being indented into the previous nested section.
  #​2364
• Removed unnecessary @import in the CSS.
  #​2260

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