Following on from T236069: Make PHP 7.3 non voting on REL1_31... As we support REL1_31 until June 2021, it would be useful to upgrade PHPCS across the REL1_31 fleet
We don't need to fix the code, just adding necessary exclusions would be sufficient
Upgrade mediawiki/mediawiki-codesniffer to 19.1.0 and ignore new rules in .phpcs.xml. Example for CentralAuth REL1_31:
https://gerrit.wikimedia.org/r/#/c/mediawiki/extensions/CentralAuth/+/538973/