Upgrade Routines Can Run on Front-End Requests

[kevinfodness]

Description of the bug

The upgrade routine in includes/class-apple-news.php that compares the currently installed version of the plugin to an option value of the last recorded version of the plugin and executes database migration code if the versions are different is not coded to prevent execution on the front-end. This upgrade code should only ever be executed in an admin context (is_admin()).

Steps To Reproduce

1. Update the source files for the plugin to a newer version which triggers an update routine (e.g., from 2.4.0 to 2.5.0) directly on the filesystem (rather than clicking an upgrade link in the admin).
2. Visit the front-end of the site while logged out and notice that the upgrade routine executes even though the current user is not logged in.

Additional Information

No response