Bump Microsoft.AspNetCore.Mvc.Testing from 6.0.0 to 8.0.0

Bumps [Microsoft.AspNetCore.Mvc.Testing](https://github.com/dotnet/aspnetcore) from 6.0.0 to 8.0.0.
- [Release notes](https://github.com/dotnet/aspnetcore/releases)
- [Changelog](https://github.com/dotnet/aspnetcore/blob/main/docs/ReleasePlanning.md)
- [Commits](dotnet/aspnetcore@v6.0.0...v8.0.0)

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

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

Source/Boxed.DotnetNewTest/Boxed.DotnetNewTest.csproj

@@ -20,11 +20,11 @@
   </ItemGroup>
 
   <ItemGroup Label="Package References (.NET 7)" Condition="'$(TargetFramework)' == 'net7.0'">
-    <PackageReference Include="Microsoft.AspNetCore.Mvc.Testing" Version="7.0.0" />
+    <PackageReference Include="Microsoft.AspNetCore.Mvc.Testing" Version="8.0.0" />
   </ItemGroup>
 
   <ItemGroup Label="Package References (.NET 6)" Condition="'$(TargetFramework)' == 'net6.0'">
-    <PackageReference Include="Microsoft.AspNetCore.Mvc.Testing" Version="6.0.0" />
+    <PackageReference Include="Microsoft.AspNetCore.Mvc.Testing" Version="8.0.0" />
   </ItemGroup>
 
   <ItemGroup Label="Files">