I think some of the weights are updating. When I sum all of the weights I get another value after training than I got before training, but it is still very close to the first one.
sum(weight) before training: tensor(1.00000e+06 *
       3.9201)
Bias[0] before training: tensor(0.3681)

sum(weight) after training:  tensor(1.00000e+06 *
       3.8118)
Bias[0] after training tensor(-47.6196)