### Steps to reproduce

1. Go to the notification center and have mulitple work packages listed

2. Open the first work package on the relations tab

3. Add a child wp (chose one that is not listed on the page already)

4. Go to the any other workpackage notification

5. open the relations tab

6. Add the child that you added before now to this WorkPackage

7. Observe the counter of the relations tab header

1. alternatively: watch the network tab in the browser console


### What is the buggy behavior?

* The counter is updated twice

* Each call, has a different work package ID assigned (first the ID of the old WP, the second request has the new WP id assigned)

* this causes the counter to flicker as it shows the number of the old WorkPackages before the correct one is rendered.

* Begin of the insertionSometimesEnd of the insertion Begin of the deletion Unfortunately,End of the deletion that Begin of the insertioncaused the counter to show the (shortly) wrong number.End of the insertion Begin of the deletion can only barely be seen, but I strongly assume that `rspec ./spec/features/work_packages/details/relations/hierarchy_spec.rb:155` flickered because of that.End of the deletion


### What is the expected behavior?

1. Only the counter for the actual WP should be loaded, not all previous WP as well


### <img class="op-uc-image op-uc-image_inline" src="/api/v3/attachments/243314/content">

<br>

### Environment information

**OpenProject version**

_15.1_

**Browser**

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

**Operating System**

* [ ] Windows
* [x] Mac OS X
* [ ] Mobile iOS
* [ ] Mobile Android
* [ ] Linux (please specify distro)
* [ ] Chrome OS
* [ ] Other (please specify)

**Language**

_German_