fix(ai-prompr-decorator): fix unable to modify request

[oowl]

Summary

Checklist

• The Pull Request has tests
• A changelog file has been created under changelog/unreleased/kong or skip-changelog label added on PR if changelog is unnecessary. README.md
• There is a user-facing docs PR against https://github.com/Kong/docs.konghq.com - PUT DOCS PR HERE

Issue reference

AG-182

[tysoekong]

Just pause for ONE SECOND on this one. I found something else....

[oowl]

cherry-pick from next/3.9 fix
#13966

[team-gateway-bot]

Cherry-pick failed for master, because it was unable to cherry-pick the commit(s).

Please cherry-pick the changes locally.

git remote add upstream https://github.com/kong/kong-ee
git fetch upstream master
git worktree add -d .worktree/cherry-pick-13965-to-master-to-upstream upstream/master
cd .worktree/cherry-pick-13965-to-master-to-upstream
git checkout -b cherry-pick-13965-to-master-to-upstream
ancref=$(git merge-base 5e6b1f05f5e5a7b9543eb64004f3bb3dac8957e5 ae24eb3adf9f3f5de7a958ea115084588510a11b)
git cherry-pick -x $ancref..ae24eb3adf9f3f5de7a958ea115084588510a11b