Fix cross-dependency between test projects

[danielskovli]

Description

During #897, for whatever reason, I needed access to something from Altinn.App.Api.Tests in Altinn.App.Core.Test: https://github.com/Altinn/app-lib-dotnet/pull/897/files#diff-368dd4a3905e2ad7d20facda4de7250f66ca9addd8cbaab95bd6f43a3ce602adR34

Refactoring around this requirement felt like a bitter and time consuming pill to swallow at the time.

At some glorious point in the future, this should be fixed.

Additional Information

I cant remember exactly what the dependency was, but simply removing the reference in Altinn.App.Api.Tests.csproj` and trying to compile the tests will probably give a good indication of what's up.

Tasks

No response

Acceptance Criterias

No response

[danielskovli]

Note to self: This test should have been placed in the Altinn.App.Core.Tests project, but had to be placed in the Altinn.App.Api.Tests project because it relies on some test data which is located there.

Perhaps test data should be moved to the Altinn.App.Common.Tests project, along with lots of other things I'm sure.