save post meta only for course post type

[bsetiawan88]

Description

Added post type check before updating post meta.

Fixes #887

How has this been tested?

Create and edit post manually within either a "course" or a "non-course" post type.

Screenshots

Types of changes

Checklist:

• [ ] This PR requires and contains at least one changelog file. <!-- To create a changelog yml file: npm run dev changelog add -- -i and follow the prompt. See also: https://github.com/gocodebox/lifterlms/blob/trunk/packages/dev/README.md#changelog-add -->
• [ ] My code has been tested.
• [ ] My code passes all existing automated tests.
• [ ] My code follows the LifterLMS Coding & Documentation Standards.