github actions: Start syncing stable_6.18.y

Author: bmastbergen

.github/workflows/sync.yml

@@ -20,6 +20,9 @@ jobs:
            - branch: stable_6.12.y
              remote: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
              remote_branch: linux-6.12.y
+           - branch: stable_6.18.y
+             remote: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
+             remote_branch: linux-6.18.y
            - branch: centos9
              remote: https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-9
              remote_branch: main