Catch mysqli_sql_exception from mysqli::begin_transaction()

[morozov]

The existing test started failing with the releases of PHP 8.5.2, PHP 8.4.17 and PHP 8.3.30 (php/php-src@dbf56e0) (example):

1) Doctrine\DBAL\Tests\Functional\TransactionTest::testBeginTransactionFailure
Failed asserting that exception of type "mysqli_sql_exception" matches expected exception "Doctrine\DBAL\Exception\ConnectionLost". Message was: "MySQL server has gone away" at
/home/runner/work/dbal/dbal/src/Driver/Mysqli/Connection.php:83
/home/runner/work/dbal/dbal/src/Connection.php:1058
/home/runner/work/dbal/dbal/tests/Functional/TransactionTest.php:29
/home/runner/work/dbal/dbal/tests/Functional/TransactionTest.php:88
/home/runner/work/dbal/dbal/tests/Functional/TransactionTest.php:28

The proposed logic is consistent with commit() and rollBack(), however I don't know if handling the return value is still needed.

UPD: starting PHP 8.1.0, the default mysqli error reporting mode is MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT (documentation), which means throwing a mysqli_sql_exception for errors from mysqli function calls (documentation).

Since we require PHP ~8.2, it means that we no longer need to check the return value. The code could be cleaned up in the next minor release.