Fix two minor bugs (MIGRATE key args and getKeysUsingCommandTable) (#9455)

1. MIGRATE has a potnetial key arg in argv[3]. It should be reflected in the command table.
2. getKeysUsingCommandTable should never free getKeysResult, it is always freed by the caller)
   The reason we never encountered this double-free bug is that almost always getKeysResult
   uses the statis buffer and doesn't allocate a new one.

(cherry picked from commit 6aa2285e32a6bc16fe2938bfb40d833db7d3752d)

src/db.c

@@ -1623,7 +1623,6 @@ int getKeysUsingCommandTable(struct redisCommand *cmd,robj **argv, int argc, get
              * return no keys and expect the command implementation to report
              * an arity or syntax error. */
             if (cmd->flags & CMD_MODULE || cmd->arity < 0) {
-                getKeysFreeResult(result);
                 result->numkeys = 0;
                 return 0;
             } else {

src/server.c

@@ -870,7 +870,7 @@ struct redisCommand redisCommandTable[] = {
 
     {"migrate",migrateCommand,-6,
      "write random @keyspace @dangerous",
-     0,migrateGetKeys,0,0,0,0,0,0},
+     0,migrateGetKeys,3,3,1,0,0,0},
 
     {"asking",askingCommand,1,
      "fast @keyspace",