build(deps): bump azure-identity from 1.20.0 to 1.21.0 in /backend
Bumps [azure-identity](https://github.com/Azure/azure-sdk-for-python) from 1.20.0 to 1.21.0.
- [Release notes](https://github.com/Azure/azure-sdk-for-python/releases)
- [Changelog](https://github.com/Azure/azure-sdk-for-python/blob/main/doc/esrp_release.md)
- [Commits](https://github.com/Azure/azure-sdk-for-python/compare/azure-identity_1.20.0...azure-identity_1.21.0)
---
updated-dependencies:
- dependency-name: azure-identity
dependency-version: 1.21.0
dependency-type: direct:production
update-type: version-update:semver-minor
...
Signed-off-by: dependabot[bot] <support@github.com>
dependabot[bot]