[llvm] Remove fork handling from release issue workflow (PR #79310)

[Nikita Popov via llvm-commits]

nikic wrote:

Another issue is that we get duplicate command executions if cherry-pick is part of the issue description and an issue subscriber comment gets posted. We can add `<!--IGNORE-->` to the start of the subscriber comments to avoid this.

https://github.com/llvm/llvm-project/pull/79310