Pipeline change webhook never contains merge request information
Hi! I'm trying to use the webhooks API, and I'm able to receive webhooks, but for any commit that triggers a pipeline, even if it's part of a merge request, the payload always contains `merge_request: null`.
Example payload:
```json
{
"object_kind": "pipeline",
"object_attributes": {
"id": 181519610,
"ref": "demo3",
"tag": false,
"sha": "031aa33c35850bee69907ede354d80db1d0b71a0",
"before_sha": "0000000000000000000000000000000000000000",
"source": "push",
"status": "success",
"detailed_status": "passed",
"stages": [
"build"
],
"created_at": "2020-08-24 23:25:33 UTC",
"finished_at": "2020-08-24 23:25:51 UTC",
"duration": 15,
"variables": [
]
},
"merge_request": null,
...
}
```
and [here](https://gitlab.com/kubukoz/demo/-/merge_requests/7/pipelines) you can see that the pipeline in question (id: 181519610) is indeed part of the merge request.
This is true for both the payload stored in the webhook log inside gitlab itself, as well as the JSON payloads that I can see in the application that receives them.
issue