Update review prompt instructions in workflow file

try to persuade claude, that we will post the comments later on, so he will not respond with things like

> Since I can't post comments on the upstream repo due to token permissions, here's the response to the reviewer's question:

Author: staabm

.github/workflows/claude-pr-review.yml

@@ -345,6 +345,7 @@ jobs:
           prompt+=$'\n'
           prompt+="Commit each logical change separately with a descriptive message."
           prompt+="Push the commits in the repo."
+          prompt+="The results of this prompt will be posted to the pull request in a separate step."
 
           {
             echo 'PROMPT<<PROMPT_DELIMITER'