Mysql upgrade to 5.7: Data too long for column
Presumably the problem is that your sql_mode variable now has STRICT in it, which means that inserts/updates with varchar values that are too long for the defined length of the columns now lead to errors, whereas previously the values were truncated without any errors.

To go back to the old behaviour, you can edit your /etc/my.cnf file, look for the sql-mode variable, and remove the STRICT keyword from it. Then either restart mysqld or just log in and set sql_mode dynamically:

SET GLOBAL sql_mode='the same value as in the .cnf file here';