chore: generate a expired certificate

When the days is zero, the expire date will be exactly the same date
that the certificate is generated.

Signed-off-by: Vitor Mattos <1079143+vitormattos@users.noreply.github.com>

Author: vitormattos

tests/JSignPDFTest.php

@@ -124,7 +124,7 @@ public function testCertificateExpired()
         mkdir('vfs://download/jsignpdf', 0755, true);
         $params->setjSignPdfJarPath('vfs://download/jsignpdf');
         $params->setJSignPdfDownloadUrl('');
-        $params->setCertificate(file_get_contents(__DIR__ . DIRECTORY_SEPARATOR . 'resources' . DIRECTORY_SEPARATOR . 'certificado.pfx'));
+        $params->setCertificate($this->getNewCert('123', 0));
         $params->setPassword('123');
         $signedFilePath = $params->getTempPdfSignedPath();
         file_put_contents($signedFilePath, 'signed file content');