Bump Microsoft.Identity.Web.UI from 2.19.1 to 2.21.1 in /src

Bumps [Microsoft.Identity.Web.UI](https://github.com/AzureAD/microsoft-identity-web) from 2.19.1 to 2.21.1.
- [Release notes](https://github.com/AzureAD/microsoft-identity-web/releases)
- [Changelog](https://github.com/AzureAD/microsoft-identity-web/blob/master/changelog.md)
- [Commits](https://github.com/AzureAD/microsoft-identity-web/commits)

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

Signed-off-by: dependabot[bot] <support@github.com>

src/IoTHub.Portal.Server/IoTHub.Portal.Server.csproj

@@ -64,7 +64,7 @@
     <PackageReference Include="Microsoft.Graph" Version="5.56.0" />
     <PackageReference Include="Microsoft.OpenApi" Version="1.6.15" />
     <PackageReference Include="Microsoft.VisualStudio.Azure.Containers.Tools.Targets" Version="1.21.0" />
-    <PackageReference Include="Microsoft.Identity.Web.UI" Version="2.19.1" />
+    <PackageReference Include="Microsoft.Identity.Web.UI" Version="2.21.1" />
     <PackageReference Include="MudBlazor" Version="6.20.0" />
     <PackageReference Include="NetEscapades.AspNetCore.SecurityHeaders" Version="0.22.0" />
     <PackageReference Include="Newtonsoft.Json" Version="13.0.3" />