Why is the Project Update Bot telling me to change this?

In regards to: 📌 Automated Drupal 11 compatibility fixes for ip2country Needs work

Since when is a $defaultTheme required in a subclass of UpdatePathTestBase ? Was the profile used by UpdatePath tests changed recently or something? I don't see any mention in the change records that this changed between D10 and D11.

This has never triggered an error or warning in D9 or D10, on Drupal CI or on Gitlab CI.

Yes, I am well aware of the old change record The 'testing' install profile's setting of a default theme (Classy) is now deprecated → , but as I said update path tests have never needed this, I assume because update path tests are run in a profile other than 'testing' or something like that?

Core Drupal 10 contains 26 subclasses of UpdatePathTestBase, and only 16 of those declare a $defaultTheme (and apparently only when needed, like with the CKEditor update tests).

For example, neither of these subclasses of UpdatePathTestBase declare a $defaultTheme:
core/modules/block_content/tests/src/Functional/Update/BlockContentRemoveConstraint.php
core/modules/block_content/tests/src/Functional/Update/BlockContentUpdateTest.php

Regardless, Rector is telling me this is wrong, but it has never been wrong in the past and is apparently OK for core to do.