barrier for tablet ... failed: seastar::broken_promise

[kbr-scylla]

This apparently happens when we have a dead node and try to do a barrier.
It doesn't seem to be harmful in any way. It's just weird that we're getting a broken_promise error instead of something more high-level.

Observed in scylladb/scylla-cluster-tests#9031

2024-10-19T09:16:26.885+00:00 longevity-large-partitions-200k-pks-db-node-26155658-0-1     !INFO | scylla[4507]:  [shard  0: gms] raft_topology - executing global topology command barrier_and_drain, excluded nodes: {}
2024-10-19T09:16:29.383+00:00 longevity-large-partitions-200k-pks-db-node-26155658-0-1      !ERR | scylla[4507]:  [shard  0: gms] raft_topology - drain rpc failed, proceed to fence old writes: std::runtime_error (raft topology: exec_global_command(barrier_and_drain) failed with seastar::rpc::closed_error (connection is closed))
2024-10-19T09:16:29.383+00:00 longevity-large-partitions-200k-pks-db-node-26155658-0-1     !INFO | scylla[4507]:  [shard  0: gms] raft_topology - updating topology state: advance fence version to 2108
2024-10-19T09:16:29.384+00:00 longevity-large-partitions-200k-pks-db-node-26155658-0-1     !INFO | scylla[4507]:  [shard  0: gms] raft_topology - executing global topology command barrier, excluded nodes: {}
2024-10-19T09:16:29.384+00:00 longevity-large-partitions-200k-pks-db-node-26155658-0-1  !WARNING | scylla[4507]:  [shard  0: gms] raft_topology - barrier for tablet 27470250-8dca-11ef-ae5d-04fec4937667:79 failed: seastar::broken_promise (broken promise)
2024-10-19T09:16:29.384+00:00 longevity-large-partitions-200k-pks-db-node-26155658-0-1      !ERR | scylla[4507]:  [shard  0: gms] raft_topology - topology change coordinator fiber got error std::runtime_error (raft topology: exec_global_command(barrier) failed with seastar::rpc::closed_error (connection is closed))