Broadcasts: Don't display next import date/time when event running

[n7studios]

Summary

When the scheduled event to import ConvertKit Broadcasts to WordPress Posts is running, the timestamp for the next scheduled event is 1, resulting in incorrect output on the description:

This PR resolves by not outputting the next scheduled date/time when the event is running:

When the event is not running, the next scheduled date/time displays in the description.

Testing

• BroadcastsToPostsCest:testBroadcastsManualImportWhenEnabled: Test that the description does not display when using the manual import functionality.

Checklist

• I have written a test and included it in this PR
• I have run all tests and they pass
• The code passes when running the PHP CodeSniffer
• Code meets WordPress Coding Standards for PHP, HTML, CSS and JS
• Security and Sanitization requirements have been followed
• I have assigned a reviewer or two to review this PR (if you're not sure who to assign, we can do this step for you)