Bump NetEscapades.AspNetCore.SecurityHeaders in /src (#2558)

Bumps [NetEscapades.AspNetCore.SecurityHeaders](https://github.com/andrewlock/NetEscapades.AspNetCore.SecurityHeaders) from 0.20.0 to 0.21.0.
- [Changelog](https://github.com/andrewlock/NetEscapades.AspNetCore.SecurityHeaders/blob/master/CHANGELOG.md)
- [Commits](andrewlock/NetEscapades.AspNetCore.SecurityHeaders@v0.20.0...v0.21.0)

---
updated-dependencies:
- dependency-name: NetEscapades.AspNetCore.SecurityHeaders
  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/IoTHub.Portal.Server/IoTHub.Portal.Server.csproj

@@ -66,7 +66,7 @@
     <PackageReference Include="Microsoft.VisualStudio.Azure.Containers.Tools.Targets" Version="1.19.5" />
     <PackageReference Include="Microsoft.Identity.Web.UI" Version="2.14.0" />
     <PackageReference Include="MudBlazor" Version="6.10.0" />
-    <PackageReference Include="NetEscapades.AspNetCore.SecurityHeaders" Version="0.20.0" />
+    <PackageReference Include="NetEscapades.AspNetCore.SecurityHeaders" Version="0.21.0" />
     <PackageReference Include="Newtonsoft.Json" Version="13.0.3" />
     <PackageReference Include="prometheus-net.AspNetCore" Version="8.0.1" />
     <PackageReference Include="Quartz.Extensions.Hosting" Version="3.7.0" />