Prevent triage agent from using unmerged pull requests

[m-blaha]

Add instructions to the prompt to check merge status in case the proposed fix comes from a pull request. Fixes from PRs that has not yet been merged will not be used for backporting.

Resolves: https://github.com/packit/jotnar/issues/229

[gemini-code-assist]

Code Review

This pull request adds an important validation step to the triage agent's prompt, preventing it from using fixes from unmerged pull requests. The change is well-implemented by adding a new instruction section and updating the subsequent step numbering. I've added one suggestion to improve the clarity and conciseness of the new instructions for the language model, which should lead to more reliable behavior.

[lbarcziova]

this looks good to me, thanks!

Since we recently discussed few times the possibility of using an unmerged fix (although in the end we avoided going this way), I'm wondering if we still might need a way how to bypass this verification step, curious what do others think. Maybe forcing the fix by attaching it directly to Jira? Which also leads me to the question, how does the new instruction 2.3 behave if the patch is coming from Jira attachment? Should we explicitly mention not to do the check for that case?

[TomasKorbar]

Could we perhaps add pull request validator tool to check the pull request? There could be parameter to allow unmerged pull requests set by default to False and we would add jira label like unmerged_allowed to switch the parameter to True.

[m-blaha]

@TomasKorbar That's a great idea - there even is an issue for something similar: https://github.com/packit/jotnar/issues/154 .