Apply T312274 to wmf wikis

1. ALTERs to run: https://gerrit.wikimedia.org/r/c/mediawiki/extensions/CentralNotice/+/817882/2/sql/mysql/patch-cn_notice_regions-unique-to-pk.sql
2. Where to run those changes: centralnotice
3. When to run those changes: any time
4. If the schema change is backwards compatible: Yes
5. If the schema change has been tested already on some of the test/beta wikis: beta already running with the new schema
6. if the data should be made available on the labs replicas and/or dumps: no change of the existing rules

Due to a bug in the schema change generator (T314138) the DROP + ALTER should be rewritten to be atomic:

alter table cn_notice_regions drop key nr_notice_id_region, ADD  PRIMARY KEY (nr_notice_id, nr_region);