Fixed assignees query name

app/assets/javascripts/vue_shared/components/sidebar/queries/get_issue_assignees.query.graphql

 #import "~/graphql_shared/fragments/user.fragment.graphql"
 #import "~/graphql_shared/fragments/user_availability.fragment.graphql"
 
-query issueParticipants($fullPath: ID!, $iid: String!) {
+query issueAssignees($fullPath: ID!, $iid: String!) {
   workspace: project(fullPath: $fullPath) {
     __typename
     issuable: issue(iid: $iid) {