Cherry pick merge commit instead of original commits (#5904)

cherry_pick_pull.sh was copied from Kubernetes which allows merge
commits. It makes sense to cherry pick original commits for Kubernetes
because the original commits can be found in both master and release
branches. However, Antrea uses squash merging at the most time,
cherry-picking original commits would cause inconsistency between master
and release branches. The commit changes to cherry pick the merge
commit.

Signed-off-by: Quan Tian <[email protected]>

hack/cherry-pick-pull.sh

@@ -162,7 +162,8 @@ gitamcleanup=true
 for pull in "${PULLS[@]}"; do
   echo "+++ Downloading patch to /tmp/${pull}.patch (in case you need to do this again)"
 
-  curl -o "/tmp/${pull}.patch" -sSL "https://github.com/${MAIN_REPO_ORG}/${MAIN_REPO_NAME}/pull/${pull}.patch"
+  merge_commit=$(gh pr view "$pull" --json mergeCommit -t '{{(printf "%s" $.mergeCommit.oid)}}')
+  curl -o "/tmp/${pull}.patch" -sSL "https://github.com/${MAIN_REPO_ORG}/${MAIN_REPO_NAME}/commit/${merge_commit}.patch"
   echo
   echo "+++ About to attempt cherry pick of PR. To reattempt:"
   echo "  $ git am -3 /tmp/${pull}.patch"