Bump Microsoft.AspNetCore.Mvc.Testing from 5.0.11 to 6.0.0 (#617)

Bumps [Microsoft.AspNetCore.Mvc.Testing](https://github.com/dotnet/aspnetcore) from 5.0.11 to 6.0.0.
- [Release notes](https://github.com/dotnet/aspnetcore/releases)
- [Commits](https://github.com/dotnet/aspnetcore/compare/v5.0.11...v6.0.0)

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

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

tests/FunctionalTests/FunctionalTests.csproj

@@ -13,7 +13,7 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.AspNetCore.Mvc.Testing" Version="5.0.11" />
+    <PackageReference Include="Microsoft.AspNetCore.Mvc.Testing" Version="6.0.0" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.0.0" />
     <PackageReference Include="xunit" Version="2.4.1" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.4.3">