test: fix Registrar for DB Config

[kenjis]

Description Fixes a serious bug in DB testing configuration.

phpunit / PHP 8.1 - MySQLi
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1) Tests\Authentication\Authenticators\HmacAuthenticatorTest::testAttemptCannotFindUser
TypeError: CodeIgniter\Database\SQLite3\Connection::_escapeString(): Argument #1 ($str) must be of type string, CodeIgniter\I18n\Time given, called in /home/runner/work/shield/shield/vendor/codeigniter4/framework/system/Database/BaseConnection.php on line 1346
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https://github.com/codeigniter4/shield/actions/runs/8600000130/job/23564066896

Checklist:

• [x] Securely signed commits
• [] Component(s) with PHPDoc blocks, only if necessary or adds value
• [] Unit testing, with >80% coverage
• [] User guide updated
• [x] Conforms to style guide