[ci] Run test_decomp parallel (#92566)
run test_decomp in parallel with itself since it now takes 2+ hours on some architectures https://docs.google.com/spreadsheets/d/1o0W4WjOYIyPSzBSl3lelvKcQyLOiv8pMijiGUDoPuBU/edit#gid=0
Pull Request resolved: https://github.com/pytorch/pytorch/pull/92566
Approved by: https://github.com/huydhn
