test: project check for unattached dataset (#115)

* fix(test): project check for unattached dataset

Datasets that are not attached to projects seem to not have the `project` attribute returned.
Adjusting the check in tests.
This also matches to how the JuliaHub api tests do this check [here](https://github.com/JuliaComputing/JuliaHub/blob/0c1d7d512219454ce99b58efd2f3587b25753242/tests/api/juliaruncloud/datasets.jl#L418).

Author: tanmaykm

test/projects-live.jl

@@ -76,7 +76,7 @@ try
         @test project_dataset.project === nothing
         @test length(project_dataset.versions) == 1
         # TODO: add this properly to DatasetVersion?
-        @test project_dataset._json["versions"][1]["project"] === nothing
+        @test !haskey(project_dataset._json["versions"][1], "project")
         @test project_dataset._json["versions"][1]["uploader"]["username"] == auth.username
 
         # The authentication object we use does not have a project associated with it