Merge bitcoindevkit/bdk#1895: ci: fix publish_docs job fails with "permission denied"

8b0b3a4de54c5a592d9b385e1d99620960b05712 grant write permission to publish_docs (Musab1258)

Pull request description:

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  ### Description

  <!-- Describe the purpose of this PR, what's being adding and/or fixed -->

  The publish_docs workflow pushes changes to this repository: "bitcoindevkit/bitcoindevkit.org" which requires valid credentials. By setting the persist-credentials to false in #1778, the credentials required are not made available.

  ### Notes to the reviewers

  <!-- In this section you can include notes directed to the reviewers, like explaining why some parts
  of the PR were done in a specific way -->

  To fix the issue I added a write permission to the publish_jobs, which will allow it to push changes without the credentials.

  ### Changelog notice

  <!-- Notice the release manager should include in the release tag message changelog -->
  <!-- See https://keepachangelog.com/en/1.0.0/ for examples -->

  ### 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

  #### New Features:

  * [ ] I've added tests for the new feature
  * [ ] I've added docs for the new feature

  #### Bugfixes:

  * [ ] This pull request breaks the existing API
  * [ ] I've added tests to reproduce the issue which are now passing
  * [ ] I'm linking the issue being fixed by this PR

ACKs for top commit:
  notmandatory:
    ACK 8b0b3a4de54c5a592d9b385e1d99620960b05712

Tree-SHA512: d72aaf79f99010b75f95404eadc61f0ce35f38cb9c24b0dcfc90dbe043affef06c477b6faa02dd488820c472bfc415993affdf67ebd55138dde0865e625ebf3d