fix: test_replication_all failure

Fixes #4150. The failure can be reproduced with high probability on ARM via
`pytest dragonfly/replication_test.py -k test_replication_all[df_factory0-mode0-8-t_replicas3-seeder_config3-2000-False]`

Not sure why this barrier is needed but #4146 removes the barrier
which breaks a gentle balance in the code in unexpected way.

Signed-off-by: Roman Gershman <roman@dragonflydb.io>

src/server/journal/executor.cc

@@ -83,6 +83,11 @@ void JournalExecutor::SelectDb(DbIndex dbid) {
     auto cmd = BuildFromParts("SELECT", dbid);
     Execute(cmd);
     ensured_dbs_[dbid] = true;
+
+    // TODO: This is a temporary fix for #4146.
+    // For some reason without this the replication breaks in regtests.
+    auto cb = [](EngineShard* shard) { return OpStatus::OK; };
+    shard_set->RunBriefInParallel(std::move(cb));
   } else {
     conn_context_.conn_state.db_index = dbid;
   }