Merge bitcoindevkit/bdk#638: Fix CI, bump MSRV to 1.56.1

Merge bitcoindevkit/bdk#638: Fix CI, bump MSRV to 1.56.1

b289c4ec2d4e19cd231e65f6e71e2b7422a81be1 Bump MSRV from 1.56.0 to 1.56.1 (Daniela Brozzoni)

Pull request description:

  ### Description
  This PR fixes the CI, which is currently failing after a Github Actions update.
  The MSRV is bumped to 1.56.1 (from 1.56.0), since that's `reqwest`'s current MSRV.

  ### 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:
  afilini:
    ACK b289c4ec2d4e19cd231e65f6e71e2b7422a81be1

Tree-SHA512: e3aa8638ffd374371037e71d1c9790dd4fb3aa29f0ade5655b47ef5184b26120ee5281cd1745612af2572beb8a6bb43f84da3d60a73b455f9652853fcf31b62d