Fix icon for errors to be consistent with the others

Signed-off-by: Côme Chilliet <come.chilliet@nextcloud.com>

core/Command/SetupChecks.php

@@ -63,7 +63,7 @@ protected function execute(InputInterface $input, OutputInterface $output): int
 						};
 						$emoji = match ($check->getSeverity()) {
 							'success' => '✓',
-							'error' => '❌',
+							'error' => '✗',
 							'warning' => '⚠',
 							default => 'ℹ',
 						};