Rename Nijigasaki's school uniform tag

BUR #25335 is pending approval.

create alias nijigasaki_academy_school_uniform -> nijigasaki_school_uniform

For some reason, the "academy" part of the tag was kept when aliased (maybe because Nijigasaki Academy was thought to be the name of the school). Let's change it to be consistent with the other Love Live! school uniform tags.

Previous attempt: forum #179206

The official website more often than not calls the school "Nijigasaki High School". That should be good enough a reason, referring to the above previous attempt.