Upgrade/Install: Use a unique error code when an update fails due to the PHP...

Upgrade/Install: Use a unique error code when an update fails due to the PHP JSON extension missing.

This allows update failures caused when the native PHP JSON extension is missing to be distinguished from updates that fail because the site does not meet the minimum PHP requirements.

Follow up of [46455].

Reviewed by desrosj, jorbin, johnbillion.
Fixes #47699.
Built from https://develop.svn.wordpress.org/trunk@46560


git-svn-id: https://core.svn.wordpress.org/trunk@46357 1a063a9b-81f0-0310-95a4-ce76da25c4cd