`a.getTime is not a function` error on WP dashboard

[kelvinballoo]

Bug Description

On a site in a zero data state for Search Console and Analytics, the Site Kit widget on the WordPress dashboard is showing an error: a.getTime is not a function

A support ticket on this was also reported : https://wordpress.org/support/topic/problem-a-gettime-is-not-a-function/

Steps to reproduce

This was tested on 1.133.0 (latest release), using tester plugin 1.13.1 Beta to enforce zero data states

• After setting up Site Kit, the error appears on the dashboard
• Same observations if I test under 1.13.0 tester plugin and also if I test under develop branch.

Screenshots

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Acceptance criteria

• The Unique Visitors chart within the Site Kit Summary dashboard widget should not error in a zero data scenario

Implementation Brief

• Update the condition in the chart when the report is zero data to provide a Date instance rather than the string reference date. This changed in 1.130.0 with changes to the reference date selector but was missed because the string was being handled automatically in other places where needed
• Merge https://github.com/google/site-kit-wp/pull/9353

Test Coverage

• No changes

QA Brief

• To reproduce, connect GA with a property in zero data state and view the SK widget on the WP dashboard
• This issue is specific to the zero data state – it isn't observable in a gathering state

Changelog entry

• Fix unexpected error in Site Kit WordPress dashboard widget for sites in zero data states.