nsys-jax CI: upload rendered notebook to GitHub Gist

[olupton]

• Every PR or push to main publishes the rendered IPython notebook to a new Gist, the URL can be found in the CI log
• The contents of this Gist is copied:
  • To https://gist.github.com/nvjax/e2cd3520201caab6b67385ed36fad3c1, if it was a push to main
  • To https://gist.github.com/nvjax/16698d9e9e52320243165d61b5bb3975, otherwise (to test the copy machinery)

Unfortunately this copies and pastes some magic, but we are right up against the reusable workflow limit.