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### Steps to reproduce

1. Login and open a team planner

2. Make sure you have two work packages in this project: A and B, predecessor and follower (with 0 lag days, i.e. follower starts immediately after the predecessor)

3. Try moving the follower's start date (drag backwards) so that it includes the finish date of the predecessor)


### What is the buggy behavior?

* Success message despite the change not being possible


### What is the expected behavior?

1. Begin of the insertionOn drag start, the dates "blocked" by predecessor are forbidden as they are in the date pickerEnd of the insertion Begin of the deletion Another type of message?End of the deletion


###

### Environment information

**OpenProject version**

_16.5_

**Browser**

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