[3.0.0-alpha] Incorrect behavior when forcing time unit to month

Expected Behavior

Using unit: 'month' for time axis should be ok whatever the data.

Current Behavior

If the intervals between data points are too short, using unit: 'month' leads to unusable chart.

Steps to Reproduce (for bugs)

Fiddle that reproduces the issue: https://jsfiddle.net/7ce1afx4/

If we remove unit: 'month', the issue is gone.
If in generateDate we add “* 30” to generate monthly points instead of daily points, the issue is gone too.

Context

I encountered this issue after migrating to 3.0.0-alpha, I think this is a regression because I never saw this with 2.9.

Environment

• Chart.js version: 3.0.0-alpha
• Browser name and version: Chromium 80