docs: fix example (#3907)

raw SQL request mode example was wrong because execute_mode should be request

Author: aceforeverd

docs/en/openmldb_sql/dql/SELECT_STATEMENT.md

@@ -142,6 +142,6 @@ Parentheses `()` expression is the minimal unit to a request row, every expressi
 -- executing SQL as request mode, with request row (10, "foo", timestamp(4000))
 SELECT id, count (val) over (partition by id order by ts rows between 10 preceding and current row)
 FROM t1
-CONFIG (execute_mode = 'online', values = (10, "foo", timestamp (4000)))
+CONFIG (execute_mode = 'request', values = (10, "foo", timestamp (4000)))
 ```
 

docs/zh/openmldb_sql/dql/SELECT_STATEMENT.md

@@ -153,7 +153,7 @@ OpenMLDB >= 0.9.0 支持在 query statement 中用 CONFIG 子句配置 SQL 的
 -- 执行请求行为 (10, "foo", timestamp(4000)) 的在线请求模式 query
 SELECT id, count (val) over (partition by id order by ts rows between 10 preceding and current row)
 FROM t1
-CONFIG (execute_mode = 'online', values = (10, "foo", timestamp (4000)))
+CONFIG (execute_mode = 'request', values = (10, "foo", timestamp (4000)))
 ```
 
 ## 离线同步模式 Query