📝 fix mypy instructions in contributing guide

[Jeitan]

Fixes #594.

Rather than drop the instructions for the now-unnecessary script, I moved it down and labeled it a previous issue. Although ideally a fresh setup would for sure be using mypy 1.16+, so if you'd prefer to drop the entire instruction I can do that too.

[jorenham]

Hmm, I suppose that since the script itself is gone, there's not really any value in keeping it. And since we're using git, it's pretty easy to look at previous versions, in case anyone is interested 🤷🏻

[Jeitan]

Okay, I'll just eliminate it then. Do you want me to remove the script, too? I left the actual script alone, but I can take out the whole shebang and all the references to it if it's truly not needed anymore.

[jorenham]

Oh I somehow thought that the script was already gone. Sorry for the confusion.

Do you want me to remove the script, too?

Yea that would help!

[Jeitan]

I squashed the doc commits and kept the deletion commit separate, not sure if that makes a difference

[jorenham]

I squashed the doc commits and kept the deletion commit separate, not sure if that makes a difference

Chique 👌🏻

[jorenham]

Thanks Andrea! And welcome aboard :)