config: fix config toml file check-mb4-value-in-utf8 problem (#9802) (

#9852)

config/config.toml.example

@@ -48,6 +48,9 @@ lower-case-table-names = 2
 # turn on this option when TiDB server is behind a proxy.
 compatible-kill-query = false
 
+# check mb4 value in utf8 is used to control whether to check the mb4 characters when the charset is utf8.
+check-mb4-value-in-utf8 = true
+
 [log]
 # Log level: debug, info, warn, error, fatal.
 level = "info"
@@ -248,6 +251,3 @@ ignore-error = false
 
 # use socket file to write binlog, for compatible with kafka version tidb-binlog.
 binlog-socket = ""
-
-# check mb4 value in utf8 is used to control whether to check the mb4 characters when the charset is utf8.
-check-mb4-value-in-utf8 = true