What non-technical qualities does a software engineer need to be successful?... Attitude? Communication skills? Vision? Teamwork? Passion?... What do you think? And why?

Patience

I mean most of the things you listed are important, but I'd say nowadays, unless you are working on your own project, teamwork is the most important.

The confidence to politely say No (when there's a good reason of course)

Wanting to learn, accepting that change is inevitable, giving proper feedback and receiving it. The last two parts alone make you a better professional than 90% of the people out there. And take responsibility for what you do.

Tenacity. Those bugs won't just jump out and introduce themselves.

Leading skills!