[Week4] Transformer Network Decoder_test/Transformer_test

Thanks for the tip. Doing it like this passes the subsequent tests and then proceeds to pass the autograder when submitted too. A shame this last lab has these inconsistencies, as noted in another thread here: Pedagogy of C5-W4-A1 (-Ex4: Encoder Layer) This makes it very confusing to finish the lab properly. Thankfully we have our helpful classmates here on Discourse to lend a hand! :grin: