Merge bitcoindevkit/bdk#1846: Fix CI

6be6d06dbd8c2b370319d3154f6fa61d75da25ad docs(chain): Fix docs for `KeychainTxOutIndex` (志宇)
5ba4d68e45e3f5503b80c73da2d413794e10b017 ci: Pin `native-tls` to `0.2.13` (志宇)

Pull request description:

  ### Description

  This PR makes CI happy again.

  * CI complained about docs here. https://github.com/bitcoindevkit/bdk/actions/runs/13420654916/job/37492201157
  * CI complained about MSRV not being satisfied. https://github.com/bitcoindevkit/bdk/actions/runs/13420654913/job/37492254119

  ### Checklists

  #### All Submissions:

  * [x] I've signed all my commits
  * [x] I followed the [contribution guidelines](https://github.com/bitcoindevkit/bdk/blob/master/CONTRIBUTING.md)
  * [x] I ran `cargo fmt` and `cargo clippy` before committing

ACKs for top commit:
  ValuedMammal:
    ACK 6be6d06d

Tree-SHA512: 87029e01c0e988863603353002c674c40cf1ebd7fa94e7430141ad49cbba770c6b7219ceb8eb001552319c8f352100b2461c8c0c1a6e977d58b8fd8e0c90d0b8