Merge bitcoindevkit/bdk#1876: ci: pin `ring` to `0.17.12` for MSRV 1.63

Merge bitcoindevkit/bdk#1876: ci: pin `ring` to `0.17.12` for MSRV 1.63

7d4128e268b7438062a1903bdbfb413f1f5b5bd0 ci: pin ring dep to 0.17.12 to fix MSRV (Steve Myers)

Pull request description:

  ### Description

  Pin `ring` to `0.17.12` for 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:
  notmandatory:
    ACK 7d4128e268b7438062a1903bdbfb413f1f5b5bd0

Tree-SHA512: c210e511955734d3c513a020ea0b7596590b048d755c026aa508f83e43ac2e2f25064a5fea1aa0e343e80b5c03bf8b52aa370dcbd708251197ca6788dac8bd66