Status dashboard check errors when backup migrate module not enabled

Problem/Motivation

If client site does not have backup migrate module enabled, status dashboard check throws following error:
Error
: Class "Drupal\backup_migrate\Entity\Schedule" not found in
status_dashboard_client_extras_status_dashboard_json_response_alter()
(line
44
of
/app/web/modules/contrib/status_dashboard_client_extras/status_dashboard_client_extras.module
).

Proposed resolution

Conditionally retrieve backup schedule data only if backup migrate module is enabled