test: add regression for array CN in signature params

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

Author: vitormattos

tests/php/Unit/Service/SignFileServiceTest.php

@@ -1166,6 +1166,14 @@ public static function providerGetSignatureParamsCommonName(): array {
 				'LibreCode',
 				'Jane Doe',
 			],
+			'array CNs should be normalized' => [
+				[
+					'issuer' => ['CN' => ['LibreCode', 'CA']],
+					'subject' => ['CN' => ['Doe', 'Jane']],
+				],
+				'LibreCode, CA',
+				'Doe, Jane',
+			],
 			'empty CNs' => [
 				[
 					'issuer' => ['CN' => ''],