feat(github): use REST for etag caching of issues

lib/modules/platform/github/graphql.ts

@@ -93,36 +93,6 @@ query($owner: String!, $name: String!, $count: Int, $cursor: String) {
 }
 `;
 
-export const getIssuesQuery = `
-query(
-  $owner: String!,
-  $name: String!,
-  $user: String!,
-  $count: Int,
-  $cursor: String
-) {
-  repository(owner: $owner, name: $name) {
-    issues(
-      orderBy: { field: UPDATED_AT, direction: DESC },
-      filterBy: { createdBy: $user },
-      first: $count,
-      after: $cursor
-    ) {
-      pageInfo {
-        endCursor
-        hasNextPage
-      }
-      nodes {
-        number
-        state
-        title
-        body
-      }
-    }
-  }
-}
-`;
-
 export const vulnerabilityAlertsQuery = (filterByState: boolean): string => `
 query($owner: String!, $name: String!) {
   repository(owner: $owner, name: $name) {