Masterbar: add_styles_and_scripts not added to admin_enqueue_scripts on Jetpack admin page

[jeherve]

Steps to reproduce the issue

1. Running master, go to Jetpack > Settings > Writing
2. Enable the masterbar
3. The page refreshes, but none of the masterbar scripts and styles are loaded on that page. They are loaded on all the other pages of the site.

[jeherve]

This may be caused by the changes that were added in #10945