fix: use faster method to fetch user count

countUsers: the actual user count reported by the backend.
countSeenUsers: count every user who was logged in once.

1: We should avoid expensive operations (like asking every backend for it's user count) in migrations.
2: The current check is wrong because countUsers returns an array. var_dump([] > 1000) => true ;)

Signed-off-by: Daniel Kesselberg <mail@danielkesselberg.de>

apps/dav/lib/Migration/Version1027Date20230504122946.php

@@ -49,7 +49,7 @@ public function __construct(private SyncService $syncService,
 	 * @param array $options
 	 */
 	public function postSchemaChange(IOutput $output, Closure $schemaClosure, array $options): void {
-		if($this->userManager->countUsers() > 1000) {
+		if($this->userManager->countSeenUsers() > 1000) {
 			$this->config->setAppValue('dav', 'needs_system_address_book_sync', 'yes');
 			$output->info('Could not sync system address books during update - too many user records have been found. Please call occ dav:sync-system-addressbook manually.');
 			return;