Converting days to weeks in Control Chart disregards working days configuration

Summary

Converting days to weeks in Control Chart disregards working days configuration.

Steps to reproduce

1. Have issue in the Kanban board which was in certain status (lets say In Progress) status from Jan 3rd to Feb 20th (total of 34 working days)
2. Configure board to have 5 working days only
   
3. Refer to Control Chart report > choose status In Progress

Expected Result

The time duration will be shown as 6 weeks 4 days, as the total working days is divided by 5 (working days configured in a week)

Actual Result

The time duration is shown as 4 weeks 6 days, the total working days is divided by 7