Merge bitcoindevkit/bdk#1613: ci: automated update to rustc 1.81.0

Merge bitcoindevkit/bdk#1613: ci: automated update to rustc 1.81.0

503f315cdde32dabbc83efd3879ac5cb26aacdbc ci: automated update to rustc 1.81.0 (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 503f315cdde32dabbc83efd3879ac5cb26aacdbc

Tree-SHA512: 60269a5525d1a0aaab400d1ef287acf1b7631ea4c2e4b1627a7d66a8a40526dce79abcd4d339dfea32ef02f573672d7d76acad10319e9336949c8ce9e92a17ad