[BugFix] GAE warning when gamma/lmbda are tensors

[louisfaury]

Description

When passing a tensor value for the discounted/exponential average weight to GAE, we'd get the warning:

UserWarning: To copy construct from a tensor, it is recommended to use sourceTensor.clone().detach() or sourceTensor.clone().detach().requires_grad_(True), rather than torch.tensor(sourceTensor)

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[pytorch-bot]

🔗 Helpful Links

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[vmoens]

LGTM thanks!