add workaround for core issue 2908210

Problem/Motivation

Any of our tests which use the test entities which have a changed time or log message are slowed down by a test field type plugin which sleep()s.

See 📌 FIx TODO in Drupal\entity_test\Plugin\Field\FieldType\ChangedTestItem Active for details.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes