Epics Roadmap's weeks start always on Sunday, even though first day of the week is Monday

Summary

Epic Roadmap's vertical week separation hairlines are between Saturday and Sunday, when they should be between Sunday and Monday, when first day of the week is Monday.

Steps to reproduce

  1. Go to Admin -> Settings -> Preferences -> Localization
  2. Make sure "Default first day of the week" is "Monday"
  3. Go to your organisations Epics Roadmap view
  4. See that the week separation hairlines are between Saturday and Sunday.

Example Project

What is the current bug behavior?

The hairlines do not respect the first day of week.

What is the expected correct behavior?

The hairlines should be between Sunday and Monday.

Relevant logs and/or screenshots

Screenshot_2021-01-08_at_12.01.38

Output of checks

Results of GitLab environment info

Expand for output related to GitLab environment info 

(For installations with omnibus-gitlab package run and paste the output of:
`sudo gitlab-rake gitlab:env:info`)

(For installations from source run and paste the output of:
`sudo -u git -H bundle exec rake gitlab:env:info RAILS_ENV=production`)

Results of GitLab application Check

Expand for output related to the GitLab application check 
(For installations with omnibus-gitlab package run and paste the output of:
sudo gitlab-rake gitlab:check SANITIZE=true)


(For installations from source run and paste the output of:
sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production SANITIZE=true)


(we will only investigate if the tests are passing)

Possible fixes