Merge bitcoindevkit/bdk#1994: ci: automated update to rustc 1.88.0

Merge bitcoindevkit/bdk#1994: ci: automated update to rustc 1.88.0

cedf9e1a01bcb6703cd543a8a791d4db4f688c82 ci: automated update to rustc 1.88.0 (Github Action)

Pull request description:

  Automated update to Github CI workflow `cont_integration.yml` by [create-pull-request](https://github.com/peter-evans/create-pull-request) GitHub action

ACKs for top commit:
  ValuedMammal:
    ACK cedf9e1a01bcb6703cd543a8a791d4db4f688c82

Tree-SHA512: 8b310912b41ec3171681c8a62f180e61e54929776e82b6221debecdd04b36c03aca5c1d83fc6261fed21807a71284cb47ed8c0ca2b7290428242c9fb618e1ed2