Nevermind I missed this part from the docs:

stride  – the stride of the window. Default value is  kernel_size

So the equation is (26+20-1(3-1)-1)/3 + 1 = 8
and not (26+20-1(3-1)-1)/1 + 1 = 24
The stride in denominator is 3 not 1. As is the case for conv2d layers.