Bump Microsoft.Graph from 4.20.0 to 4.21.0 in /src (#464)

Bumps [Microsoft.Graph](https://github.com/microsoftgraph/msgraph-sdk-dotnet) from 4.20.0 to 4.21.0.
- [Release notes](https://github.com/microsoftgraph/msgraph-sdk-dotnet/releases)
- [Commits](microsoftgraph/msgraph-sdk-dotnet@4.20.0...4.21.0)

---
updated-dependencies:
- dependency-name: Microsoft.Graph
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

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

src/AzureIoTHub.Portal/Server/AzureIoTHub.Portal.Server.csproj

@@ -22,7 +22,7 @@
     <PackageReference Include="Microsoft.Azure.Devices.Provisioning.Service" Version="1.18.1" />
     <PackageReference Include="Microsoft.Azure.Devices.Shared" Version="1.30.1" />
     <PackageReference Include="Microsoft.Extensions.Http.Polly" Version="6.0.3" />
-    <PackageReference Include="Microsoft.Graph" Version="4.20.0" />
+    <PackageReference Include="Microsoft.Graph" Version="4.21.0" />
     <PackageReference Include="Microsoft.OpenApi" Version="1.2.3" />
     <PackageReference Include="Microsoft.VisualStudio.Azure.Containers.Tools.Targets" Version="1.14.0" />
     <PackageReference Include="MudBlazor" Version="6.0.7" />