innodb_redo_log_encrypt must throw an error while setting invalid values

It is noticed while testing PS-4556, that below queries are actually executable

set global innodb_redo_log_encrypt =2;
set global innodb_redo_log_encrypt =3;
set global innodb_redo_log_encrypt =true;

However, as per functionality the only supported values must be
ON, OFF, master_key, keyring_key

Values 1,2,3,true,on all sets the value to "on"

Ideally, setting these values make no sense and must be restricted.

 

Second observation is:
mysql> show global variables like 'innodb%encrypt%';
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For the sake of uniformity, the default value must be in uppercase "OFF"