deps: Bump Microsoft.AspNetCore.Mvc.Testing from 8.0.0 to 8.0.21 (#465)

---
updated-dependencies:
- dependency-name: Microsoft.AspNetCore.Mvc.Testing
  dependency-version: 8.0.21
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Franklin Moormann <cheatcountry@gmail.com>

Author: dependabot[bot]

tests/AiDotNet.Serving.Tests/AiDotNet.Serving.Tests.csproj

@@ -9,7 +9,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.AspNetCore.Mvc.Testing" Version="8.0.0" />
+    <PackageReference Include="Microsoft.AspNetCore.Mvc.Testing" Version="8.0.21" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.14.1" />
     <PackageReference Include="xunit" Version="2.9.3" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.8.2">