Bump Azure.Identity and Microsoft.Azure.SignalR in /src/backend.tests (…

…#969)

Bumps [Azure.Identity](https://github.com/Azure/azure-sdk-for-net) and [Microsoft.Azure.SignalR](https://github.com/azure/azure-signalr). These dependencies needed to be updated together.

Updates `Azure.Identity` from 1.13.1 to 1.11.4
- [Release notes](https://github.com/Azure/azure-sdk-for-net/releases)
- [Commits](Azure/azure-sdk-for-net@Azure.Identity_1.13.1...Azure.Identity_1.11.4)

Updates `Microsoft.Azure.SignalR` from 1.28.0 to 1.29.0
- [Release notes](https://github.com/azure/azure-signalr/releases)
- [Commits](Azure/azure-signalr@v1.28.0...v1.29.0)

---
updated-dependencies:
- dependency-name: Azure.Identity
  dependency-type: direct:production
  update-type: version-update:semver-minor
- dependency-name: Microsoft.Azure.SignalR
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: polatengin <[email protected]>