using MySQL 5.5 and 5.6 clients connecting with a passwordless account to tidb fail

## Bug Report

Please answer these questions before submitting your issue. Thanks!

### 1. Minimal reproduce step (Required)

1. download 5.5 and 5.6 version MySQL client
dbdeployer downloads get-unpack mysql-5.5.62.tar.xz
dbdeployer downloads get-unpack mysql-5.6.44.tar.xz
2. create use nopw with no password,
CREATE USER 'nopw'@'%' IDENTIFIED WITH mysql_native_password
3. use 5.5 and 5.6 MySQL client connect to tidb nightly version(v5.5.0-nightly-20220208) with this "nopw" user

### 2. What did you expect to see? (Required)
connect successully
### 3. What did you see instead (Required)
root@wkload-0:/upgrade-test# /root/opt/mysql/5.5.62/bin/mysql -u nopw -h tiup-peer -P3390
ERROR 2012 (HY000): Error in server handshake

### 4. What is your TiDB version? (Required)

v5.5.0-nightly-20220208