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

[Danny Mösch via llvm-commits]

================
@@ -26,8 +26,8 @@
 
 This issue may be a good introductory issue for people new to working on LLVM. If you would like to work on this issue, your first steps are:
 
-1. Check that no other contributor has already been assigned to this issue. If you believe that no one is actually working on it despite an assignment, ping the person. After one week without a response, the assignee may be changed.
-1. In the comments of this issue, request for it to be assigned to you, or just create a [pull request](https://github.com/llvm/llvm-project/pulls) after following the steps below. [Mention](https://docs.github.com/en/issues/tracking-your-work-with-issues/linking-a-pull-request-to-an-issue) this issue in the description of the pull request.
+1. Check that no other contributor is working this issue. If someone is assigned to the issue or claimed to be working on it, ping the person. After one week without a response, the assignee may be changed.
----------------
SimplyDanny wrote:

```suggestion
1. Check that no other contributor is working on this issue. If someone is assigned to the issue or claimed to be working on it, ping the person. After one week without a response, the assignee may be changed.
```

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