Fixes pagination not always working in merge request dashboard

What does this MR do and why?

Fixes a bug where sometimes the load more button would not show the extra merge requests.

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

app/assets/javascripts/merge_request_dashboard/components/merge_requests_query.vue

 <script>
-import produce from 'immer';
 import reviewerQuery from '../queries/reviewer.query.graphql';
 import assigneeQuery from '../queries/assignee.query.graphql';
 import assigneeOrReviewerQuery from '../queries/assignee_or_reviewer.query.graphql';
@@ -64,14 +63,6 @@ export default {
           perPage: PER_PAGE,
           afterCursor: this.mergeRequests?.pageInfo?.endCursor,
         },
-        updateQuery(previousResult, { fetchMoreResult }) {
-          const { mergeRequests } = fetchMoreResult.currentUser;
-
-          return produce(fetchMoreResult, (draft) => {
-            draft.currentUser.mergeRequests.pageInfo = mergeRequests.pageInfo;
-            draft.currentUser.mergeRequests.nodes = mergeRequests.nodes;
-          });
-        },
       });
     },
   },