Fix return type of `Kernel.covar_dist`
I believe this is always a Tensor.
@@ -289,7 +289,7 @@ class Kernel(Module):
dist_postprocess_func: Callable = default_postprocess_script,
postprocess: bool = True,
**params,
- ) -> Union[Tensor, LinearOperator]:
+ ) -> Tensor:
r"""
This is a helper method for computing the Euclidean distance between
all pairs of points in :math:`\mathbf x_1` and :math:`\mathbf x_2`.
