fix(ci): preserve DCO signatures in backports (#2015)

Signed-off-by: Erez Freiberger <enoodle@gmail.com>

Author: enoodle

.github/workflows/backport.yaml

@@ -21,6 +21,7 @@ jobs:
         with:
           github_token: ${{ secrets.KAIBOT_TOKEN }}
           pull_title: "${pull_title}"
+          cherry_picking: pull_request_head
           # Backports carry the original PR's changie fragment (a new file, so no conflict).
           # Propagate changelog-exemption labels so exempt PRs still pass validate-changelog.
           copy_labels_pattern: "skip-changelog|dependencies"