Verify that `IFormDataWrapper` function `Set()` works

[olemartinorg]

I originally made the Set() function in #17187, but it was moved to (and work continued) in Altinn/app-lib-dotnet#1630. When that has been synced into the monorepo, we should check to make sure the upgrade script from #17097 generates code that is compatible with the Set() function that was finalized.