simple protocol decoder set index column incorrectly

[3AceShowHand]

What did you do?

`CREATE TABLE test.sbtest3 (
	  id int(11) NOT NULL,
	  k int(11) NOT NULL DEFAULT '0',
	  PRIMARY KEY (id),
	  KEY k_3 (k)
	)`

What did you expect to see?

the column k is not handle key column

What did you see instead?

the column k is set as handle key column, since the key k_3 id is 0, identical to the handle key column id

Versions of the cluster

Upstream TiDB cluster version (execute SELECT tidb_version(); in a MySQL client):

(paste TiDB cluster version here)

Upstream TiKV version (execute tikv-server --version):

(paste TiKV version here)

TiCDC version (execute cdc version):

(paste TiCDC version here)

[3AceShowHand]

This only affect kafka test stability, no need to block release