Hello Carley, the page_restrictions column is no longer used within
MediaWiki, see
https://phabricator.wikimedia.org/T218446
The column is being removed from the page table, a change that is almost
complete; you can track the progress of that here
https://phabricator.wikimedia.org/T60674 if you are interested. You can use
the page_restrictions table instead.
The Manual page you refer to will likely be updated once the schema change
is complete.
Thank you,
Hannah Okwelum