Fix default value for files_no_background_scan

The value is read in https://github.com/nextcloud/server/blob/b888c6146327d842e21988b0d90d6ade4f3a9435/apps/files/lib/BackgroundJob/ScanFiles.php#L105 and the default value is false.

Signed-off-by: max-nextcloud <max@nextcloud.com>

config/config.sample.php

@@ -2223,7 +2223,7 @@ $CONFIG = [
  * scan to sync filesystem and database. Only users with unscanned files
  * (size < 0 in filecache) are included. Maximum 500 users per job.
  *
- * Defaults to ``true``
+ * Defaults to ``false``
  */
 'files_no_background_scan' => false,