Separate CUDA-dependent tests

[marcoq]

Separate CUDA-dependent tests.
Then, activate the separate CUDA-dependent tests if CUDA is available.
Otherwise, run on a CPU device.

Example CUDA-dependent tests:

• GNNGraphs/test/query.jl "degreeGPU"
• GNNGraphs/test/temporalsnapshotsgraph.jl "gpu()"
• GNNlib/test/msgpass.jl "propagateGPU"
• GraphNeuralNetworks/test/examples/node_classification_cora.jl "training example GPU"
• GraphNeuralNetworks/test/layers/conv.jl "* GPU"

[CarloLucibello]

What's the meaning of this? Are you human?