Disputes: Fix reserved keyword variable names phpcs reports

[reykjalin]

Part of #8438.

Description

Remove all the Universal.NamingConventions.NoReservedKeywordParameterNames excludes from phpcs.xml.dist and fix the issues reported when running npm run lint:php in the following files:

• includes/core/server/request/class-list-disputes.php
• includes/core/server/request/class-list-documents.php

[haszari]

Upgrading to medium. Low risk but important to tidy up and should be relatively straightforward.