[llvm] [Github] Tweak the good-first-issue message not to require assignment. (PR #139858)

[Aiden Grossman via llvm-commits]

https://github.com/boomanaiden154 commented:

I think this makes a lot of sense. This is probably one of the biggest issues I see with the good-first-issue label. I think this approach will address most of the problems, so I am in favor assuming others do not have major objections.

https://github.com/llvm/llvm-project/pull/139858