Add back Drupal\Tests\migrate\Kernel\MigrateSourceTestBase::providerSource()

Problem/Motivation

📌 Remove Drupal\Tests\migrate\Kernel\MigrateSourceTestBase::providerSource() Fixed allows modules to be compatible with both 10.2 and 10.3, once 10.2 is going out of support (so 10.4 and 11.0 or 11.1), we can add the method back.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet