Update Rust crate mdbook to ^0.4.25

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
mdbook	dependencies	patch	^0.4.24 -> ^0.4.25

---

Release Notes

rust-lang/mdBook

### [`v0.4.25`](https://togithub.com/rust-lang/mdBook/blob/HEAD/CHANGELOG.md#mdBook-0425) [Compare Source](https://togithub.com/rust-lang/mdBook/compare/v0.4.24...v0.4.25) [e14d381...1ba74a3](https://togithub.com/rust-lang/mdBook/compare/e14d381...1ba74a3) ##### Fixed - Fixed a regression where `mdbook test -L deps path-to-book` would not work. [#​1959](https://togithub.com/rust-lang/mdBook/pull/1959)

---

Configuration

📅 Schedule: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined).

🚦 Automerge: Disabled by config. Please merge this manually once you are satisfied.

♻ Rebasing: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox.

🔕 Ignore: Close this PR and you won't be reminded about this update again.

---

• [ ] If you want to rebase/retry this PR, check this box

---

This PR has been generated by Mend Renovate. View repository job log here.