MySQL on PHP 8 now errors when committing or rolling back when there is no active transaction

Problem/Motivation

This @todo exists in Drupal\KernelTests\Core\Database\TransactionTest::testTransactionWithDdlStatement()

      try {
        $transaction->rollback();
        unset($transaction);
        // @TODO: an exception should be triggered here, but is not, because
        // "ROLLBACK" fails silently in MySQL if there is no transaction active.
        // $this->fail(t('Rolling back a transaction containing DDL should fail.'));
      }

This has been fixed in PHP 8.0 due to https://github.com/php/php-src/commit/990bb34891c83d12c5129fd781893704f9...

Now we have to deal with the fact that PHP 7 and PHP 8 behave in different ways.

Proposed resolution

Remaining tasks

User interface changes

None

API changes

Data model changes

None

Release notes snippet