ignore mysql schema on replication before moving from mysql 5.6 to mysql 5.7
Should I need to ignore mysql db before upgrading mysql 5.6 to 5.7 on this slave?


No, you should not.  MySQL should handle everything correctly when the replica is newer than the master by not more than one major release, e.g. 5.6 to 5.7 -- just like you have here.

The fact you appear to be using the ROW binlog format is good, but be sure you're using it on the master, too, for the best chance of continuous clean replication.

And do have a good cry while reading the official list of caveats and breaking changes.  Most of them are well-intentioned, at least.