A decommissioned node is removed from a raft config after operation is
marked as completed. This is required since otherwise the decommissioned
node will not see that decommission has completed (the status is
propagated through raft). But right after the decommission is marked as
completed a decommissioned node may terminate, so in case of a two node
cluster, the configuration change that removes it from the raft will fail,
because there will no be quorum.
The solution is to mark the decommissioning node as non voter before
reporting the operation as completed.
Fixes: #24026
Backport to 2025.2 because it fixes a potential hang. Don't backport to
branches older than 2025.2 because they don't have
8b186ab0ff, which caused this issue.
Closesscylladb/scylladb#24027
(cherry picked from commit c6e1758457)
Closesscylladb/scylladb#24093
dd9ec03323