Prepare migration for the 3.4 release

[jonasraoni]

It's needed to update the migration file due to the merge of localization folders.

A migration for the 3.4 already exists (it's working with a "lock file" as we don't have access to the previous/current version at the moment the code is called):
https://github.com/pkp/customLocale/blob/579c394dedbcfb084d0466bdf32372bcc8794a0e/classes/migration/upgrade/v1_2_0/I15_LocaleMigration.php

• Also, at this moment the build is broken with the message: CypressError: cy.click()can only be called on a single element. Your subject contained 2 elements. Pass{ multiple: true } if you want to serially click each element. Fixed by Updated deprecated string interpolation #24