Use noreply@ as email address for share emails

Fixes #26683

Before it used the instance name, which a) doesn't make sense to randomly guess email addresses and b) could contain characters that are not allowed in email addresses like spaces.

Signed-off-by: Morris Jobke <hey@morrisjobke.de>

lib/private/Share20/Manager.php

@@ -910,7 +910,7 @@ protected function sendMailNotification(IL10N $l,
 				$instanceName
 			]
 		);
-		$message->setFrom([\OCP\Util::getDefaultEmailAddress($instanceName) => $senderName]);
+		$message->setFrom([\OCP\Util::getDefaultEmailAddress('noreply') => $senderName]);
 
 		// The "Reply-To" is set to the sharer if an mail address is configured
 		// also the default footer contains a "Do not reply" which needs to be adjusted.