### Steps to reproduce

1. Do a new installation, or run `rails db:seed`
2. Open "Demo project" or "Scrum project" and go to Gantt chart view

### What is the buggy behavior?

* Work package duration is wrong for some work Begin of the insertionpackages:End of the insertion Begin of the deletion packages: End of the deletion
* for instance "Setup conference website" is reported to be 11 days long, but it should be 7 days as "working days only" is active.
* Some work packages start or finish on a non-working day, despite have "working days only" active

### What is the expected behavior?

1. Right duration
2. No start or finish dates on non-working days

### Screenshots and other files

Begin of the insertionDemo project v12.2.4

End of the insertion <img class="op-uc-image op-uc-image_inline" Begin of the insertionsrc="/api/v3/attachments/38955/content">

Scrum project v12.2.4

<img class="op-uc-image op-uc-image_inline" src="/api/v3/attachments/38956/content">

Issues v12.3.0 (not released yet)

<img class="op-uc-image op-uc-image_inline"End of the insertion src="/api/v3/attachments/38934/content"> Begin of the deletion



End of the deletion <img class="op-uc-image op-uc-image_inline" src="/api/v3/attachments/38935/content"> Begin of the insertion

End of the insertion Begin of the deletion



End of the deletion ### Environment information

**OpenProject installation type**

* [ ] Hosted cloud edition
* [ ] Packaged installation
* What distribution?
* [ ] Docker All-in-one container
* [ ] Docker-compose installation
* [x] Other (please specify)

**OpenProject version**

Using pre-12.3.0 dev branch.

**Browser**

* [ ] Chrome
* [x] Firefox
* [ ] Safari
* [ ] Mobile Safari
* [ ] Other (please specify)