Merge bitcoindevkit/bdk#2018: ci: pin `socket2` for msrv

520b116c0d0cafd03522b50dd9f0469cb6d34d6d ci: pin `socket2` for msrv (Wei Chen)

Pull request description:

  ### Description

  Pin `socket2@0.6.0` to `0.5.10` for MSRV.

  ### Changelog notice

  * Pin `socket2@0.6.0` to `0.5.10` for MSRV.

  ### Checklists

  #### All Submissions:

  * [x] I followed the [contribution guidelines](https://github.com/bitcoindevkit/bdk/blob/master/CONTRIBUTING.md)

ACKs for top commit:
  evanlinjin:
    ACK 520b116c0d0cafd03522b50dd9f0469cb6d34d6d

Tree-SHA512: ef3f4519795c166b3c464dc6d9273526a9516ddd2a0810eff3a4ddffd0ad1fd51dbe722a600cab1ce6822b222284cda981d4ca3fe1e815be957e4d34149154b1