Check that due date is not None, prevents taks without due dates from breaking Calendar API

Breaking change

Proposed change

The Todoist integration throws an error in the async_get_events method if there is a task without a due date, preventing them for working correctly with the Calendar API. This PR adds a check that the due date is not None before checking if the due date is within the date range being requested.

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Example entry for configuration.yaml:

# Example configuration.yaml

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue: 35921
• Link to documentation pull request:

Checklist

• The code change is tested and works locally.
• Local tests pass. Your PR cannot be merged unless tests pass
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• Tests have been added to verify that the new code works.

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  Updated and included derived files by running: python3 -m script.hassfest.
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  Updated by running python3 -m script.gen_requirements_all.
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