docs: move topic drop to early phase in python tmq example (#18350)

* docs: update examples/python/tmq_example.py with connector repo

* Update tmq_example.py

* docs: remove tb variable after get_table_name removed

* docs: move topic drop to early phase
Co-authored-by: NLiu Jicong <liujicong@qq.com>

docs/examples/python/tmq_example.py

@@ -4,6 +4,7 @@ from taos.tmq import *
 conn = taos.connect()
 
 print("init")
+conn.execute("drop topic if exists topic_ctb_column")
 conn.execute("drop database if exists py_tmq")
 conn.execute("create database if not exists py_tmq vgroups 2")
 conn.select_db("py_tmq")
@@ -15,7 +16,6 @@ conn.execute("create table if not exists tb2 using stb1 tags(2)")
 conn.execute("create table if not exists tb3 using stb1 tags(3)")
 
 print("create topic")
-conn.execute("drop topic if exists topic_ctb_column")
 conn.execute(
     "create topic if not exists topic_ctb_column as select ts, c1, c2, c3 from stb1"
 )