fix: Do not preempt on dispatcher fiber (#4323)

Author: chakaz

src/server/dflycmd.cc

@@ -434,7 +434,7 @@ void DflyCmd::TakeOver(CmdArgList args, RedisReplyBuilder* rb, ConnectionContext
   // We need to await for all dispatches to finish: Otherwise a transaction might be scheduled
   // after this function exits but before the actual shutdown.
   facade::DispatchTracker tracker{sf_->GetNonPriviligedListeners(), cntx->conn()};
-  shard_set->pool()->AwaitBrief([&](unsigned index, auto* pb) {
+  shard_set->pool()->AwaitFiberOnAll([&](unsigned index, auto* pb) {
     sf_->CancelBlockingOnThread();
     tracker.TrackOnThread();
   });

src/server/server_family.cc

@@ -727,7 +727,7 @@ std::optional<fb2::Fiber> Pause(std::vector<facade::Listener*> listeners, Namesp
   //    command that did not pause on the new state yet we will pause after waking up.
   DispatchTracker tracker{std::move(listeners), conn, true /* ignore paused commands */,
                           true /*ignore blocking*/};
-  shard_set->pool()->AwaitBrief([&tracker, pause_state](unsigned, util::ProactorBase*) {
+  shard_set->pool()->AwaitFiberOnAll([&tracker, pause_state](unsigned, util::ProactorBase*) {
     // Commands don't suspend before checking the pause state, so
     // it's impossible to deadlock on waiting for a command that will be paused.
     tracker.TrackOnThread();