Bump @azure/identity and azure-iothub (#665)

Bumps [@azure/identity](https://github.com/Azure/azure-sdk-for-js) to 4.2.1 and updates ancestor dependency [azure-iothub](https://github.com/Azure/azure-iot-hub-node). These dependencies need to be updated together.


Updates `@azure/identity` from 2.1.0 to 4.2.1
- [Release notes](https://github.com/Azure/azure-sdk-for-js/releases)
- [Changelog](https://github.com/Azure/azure-sdk-for-js/blob/main/documentation/Changelog-for-next-generation.md)
- [Commits](https://github.com/Azure/azure-sdk-for-js/compare/@azure/identity_2.1.0...@azure/identity_4.2.1)

Updates `azure-iothub` from 1.16.4 to 1.16.5
- [Commits](https://github.com/Azure/azure-iot-hub-node/commits)

---
updated-dependencies:
- dependency-name: "@azure/identity"
  dependency-type: indirect
- dependency-name: azure-iothub
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>