How to disable all scheduled jobs in civicrm.settings.php?
There's a new feature in the latest 4.7 that allows you to configure your site as non-production, which should do a bunch of things like this.

https://docs.civicrm.org/sysadmin/en/latest/misc/staging-production/

If you're using an older version of CiviCRM, you can manually disable all the jobs with this sql:

UPDATE civicrm_job SET is_active = 0;

But you'd want to make sure (manually) that some don't get auto-enabled (e.g. via the managed record feature in an extension).

Ultimately, the safest way to run a non-production site is in some kind of container that doesn't allow outgoing requests/emails.