Fix example value for Todoist service

[boralyl]

Description:

This PR fixes the example value for the todoist new_task service. Something in homeassistant changed between 0.102.3 and 0.103.0 that now parses the due_date as a datetime.date instead of a str. Quotes are now uses to ensure it gets parsed as a str.

This caused the homeassistant.components.websocket_api component to not be able to serialize the service ( example error). This unfortunately completely breaks the UI and the only way to get around it is to remove the component from configuration.yaml

Related issue (if applicable): fixes #29876

Checklist:

• The code change is tested and works locally.
• Local tests pass with tox. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• I have followed the [development checklist][dev-checklist]

[frenck]

Thanks, @boralyl! 👍