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

New contributors can just indicate that they are working on the issue
without requesting assignment.

That shouldd reduce the burden of assigned issues that are not actually
being worked on, and new contributors waiting for a maintainer to
asssign them the issue.

---------

Co-authored-by: Danny Mösch <[email protected]>

Author: cor3ntin

llvm/utils/git/github-automation.py

@@ -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 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.
+1. Leave a comment indicating that you are working on the issue, 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. Fix the issue locally.
 1. [Run the test suite](https://llvm.org/docs/TestingGuide.html#unit-and-regression-tests) locally. Remember that the subdirectories under `test/` create fine-grained testing targets, so you can e.g. use `make check-clang-ast` to only run Clang's AST tests.
 1. Create a Git commit.