Twenty Nineteen: Align font family of Calendar block in editor with the front end.

This commit addresses a visual inconsistency in the Twenty Nineteen theme where the Calendar block (`.wp-calendar-table`) displayed a different font family in the block editor compared to the front end.

Props rishabhwp, viralsampat, khushipatel15, sabernhardt, arshitrajyaguru97, SirLouen, SergeyBiryukov.
Fixes #63331.

git-svn-id: https://develop.svn.wordpress.org/trunk@61384 602fd350-edb4-49c9-b593-d223f7449a82

Author: SergeyBiryukov