Consider adding package unit tests to the multisite phpunit config file

We aren't running the package unit tests in the multisite test configuration. Consider whether it makes sense to add them.

No file path or test command is named. Locate the multisite PHPUnit configuration and the package unit-test definitions, then compare what the multisite configuration currently includes. Done means resolving whether package tests belong there and, if so, updating the configuration and verifying the relevant test run.

Written by the indexing model from the issue text.