QN: leaderSetEvents lack leader info

Triage why `leaderSetEvents` do no longer contain worker info. They did until at least 2024-10:
```
query {
leaderSetEvents(orderBy: createdAt_DESC) {
worker {
membershipId
}
groupId
createdAt
inBlock
}
}
```

```
"data": {
"leaderSetEvents": [
{
"worker": null,
"groupId": "contentWorkingGroup",
"createdAt": "2025-10-27T08:32:12.000Z",
"inBlock": 15102873
},
{
"worker": null,
"groupId": "operationsWorkingGroupAlpha",
"createdAt": "2025-10-17T11:13:54.000Z",
"inBlock": 14960586
},
{
"worker": null,
"groupId": "operationsWorkingGroupBeta",
"createdAt": "2025-10-06T18:55:24.001Z",
"inBlock": 14807011
},
{
"worker": null,
"groupId": "appWorkingGroup",
"createdAt": "2025-09-29T09:54:00.000Z",
"inBlock": 14701273
},
{
"worker": null,
"groupId": "operationsWorkingGroupGamma",
"createdAt": "2025-02-12T08:48:36.000Z",
"inBlock": 11422502
},
{
"worker": {
"membershipId": "515"
},
"groupId": "operationsWorkingGroupAlpha",
"createdAt": "2024-10-07T23:03:48.000Z",
"inBlock": 9591973
},
{
"worker": {
"membershipId": "515"
},
"groupId": "storageWorkingGroup",
"createdAt": "2024-09-22T20:05:30.000Z",
"inBlock": 9374586
},
{
"worker": {
"membershipId": "515"
},
"groupId": "distributionWorkingGroup",
"createdAt": "2024-09-17T20:31:12.001Z",
"inBlock": 9302981
},
{
"worker": {
"membershipId": "67206"
},
"groupId": "contentWorkingGroup",
"createdAt": "2024-07-10T20:39:12.000Z",
"inBlock": 8312388
},
{
"worker": {
"membershipId": "4129"
},
"groupId": "appWorkingGroup",
"createdAt": "2024-06-25T15:23:24.000Z",
"inBlock": 8094114
},
```

Also as example the event executed in block 9591973 contains the wrong member id. It followed execution of [proposal 1019](https://dao.l1.media/#/proposals/preview/1019) which elected [lezek](https://dao.l1.media/#/members/336) (member 336). Was it left blank intentionally?
```
{
"worker": {
"membershipId": "515"
},
"groupId": "operationsWorkingGroupAlpha",
"createdAt": "2024-10-07T23:03:48.000Z",
"inBlock": 9591973
},
```
Related code: https://github.com/Joystream/joystream/blob/b956002127ecff2c77321d149cc06af4f7afea12/tests/network-tests/src/graphql/queries/workingGroupsEvents.graphql#L59