Add more unit tests for Emeritus API Ingestion

[asadali145]

Description/Context

We worked on https://github.com/mitodl/hq/issues/4032 and added minimal unit tests. We should add some more tests to make it robust.

Here are a few tests that we will add:

• Add tests for the task courses.tasks.task_sync_emeritus_course_runs
• Add tests for mitxpro.utils.clean_url and mitxpro.utils.strip_datetime
• Add tests for the stats in courses.sync_external_courses.emeritus_api.update_emeritus_course_runs
• Add test for courses.sync_external_courses.emeritus_api.create_or_update_emeritus_course_run when existing course run start and end dates are Null.
• Add tests for the return values of:
  • courses.sync_external_courses.emeritus_api.update_emeritus_course_runs
  • courses.sync_external_courses.emeritus_api.create_or_update_emeritus_course_page
  • courses.sync_external_courses.emeritus_api.create_or_update_emeritus_course_run