Merge bitcoindevkit/bdk#1580: ci: add token for cron-update-rust.yml

b140b32648241884e0e5e222fd7a0fc4e05908f1 ci: gpg commit signing for cron-update-rust.yml (Steve Myers)
054d1483bb19e8415745033853ae0fa6943f01d9 ci: add token for cron-update-rust.yml (Steve Myers)

Pull request description:

  ### Description

  Add organization app token and GPG signing key for cron-update-rust.yml.

  ### Notes to the reviewers

  I went with the organization github app token option mentioned here:
  https://github.com/peter-evans/create-pull-request/blob/main/docs/concepts-guidelines.md#triggering-further-workflow-runs

  I added gpg commit signing with below instructions. The instructions say to use PAT for signing but the plugin doesn't mention it's needed so I want to try it with only the github app token.
  https://github.com/peter-evans/create-pull-request/blob/main/docs/concepts-guidelines.md#gpg-commit-signature-verification

ACKs for top commit:
  oleonardolima:
    ACK b140b32648241884e0e5e222fd7a0fc4e05908f1
  ValuedMammal:
    ACK b140b32648241884e0e5e222fd7a0fc4e05908f1

Tree-SHA512: 0730264ccd39645bbfe496abb43e5ac4c16de1ca9032ede4310ec190c4441152fa8adef09cf73c28c9b547d0de41e34431df88deba7d706389df564907081583