EntityManager::setEntityInstanceSettings() may work improperly for multiple variants

Problem/Motivation

If $override is FALSE for one variant, then it removes the entity overrides for all other variants.

Steps to reproduce

Tests are failing with error:

1) Drupal\Tests\simple_sitemap\Functional\SimplesitemapTest::testSetEntityInstanceSettings
Behat\Mink\Exception\ExpectationException: The string "node/2" appears in the HTML response of this page, but it should not.

Proposed resolution

Process only one variant at a time.