Pretty print tensors in `trainer.test()`
🐛 Bug
When printing the results of trainer.test() (saying "DATALOADER:0 TEST RESULTS"), it shows "tensor(...)", sometimes also including the device, when just a number should be shown.
Please reproduce using the BoringModel and post here
I copied the template and didn't modify it, as it already shows the issue: https://colab.research.google.com/drive/1_lBgEkebPAdoZ-045qGpjUG_E4IUL60w?usp=sharing

It shows this:
DATALOADER:0 TEST RESULTS
{'fake_test_acc': tensor(4.7004e-14)}

Expected behavior
DATALOADER:0 TEST RESULTS
{'fake_test_acc': 4.7004e-14}