Database dump for upgrade path has been updated

Since Drupal 9 won't be able to run updates from 8.7.x or earlier databases anymore, it is necessary for all new updates added to the code base to be tested from a Drupal 8.8.x starting point. Two new database dumps have been added, drupal-8.8.0.bare.standard.php.gz and drupal-8.8.0.filled.standard.php.gz, which must be used in D9 instead of drupal-8.bare.standard.php.gz and drupal-8.filled.standard.php.gz.

Pre-8.8.0 updates in Drupal core modules and the old database dumps are removed from Drupal 9 in #3087644: Remove Drupal 8 updates up to and including 88**.

Before 9.0.0

class MyUpdatePathTest extends UpdatePathTestBase {

  /**
   * {@inheritdoc}
   */
  protected function setDatabaseDumpFiles() {
    $this->databaseDumpFiles = [
      __DIR__ . '/../../../../modules/system/tests/fixtures/update/drupal-8.bare.standard.php.gz',
    ];
  }

After 9.0.0

class MyUpdatePathTest extends UpdatePathTestBase {

  /**
   * {@inheritdoc}
   */
  protected function setDatabaseDumpFiles() {
    $this->databaseDumpFiles = [
      __DIR__ . '/../../../../modules/system/tests/fixtures/update/drupal-8.8.0.bare.standard.php.gz',
    ];
  }