Fix slow spec in `spec/frontend/issuable_spec.js` | Issuable › initBulkUpdate › should set bulkUpdateSidebar

Job #735917811 failed for 5b8bf5dc:

Trace

FAIL spec/frontend/issuable_spec.js (8.208s)
  ● Issuable › initBulkUpdate › should set bulkUpdateSidebar
    Test took too long (6551.303706ms > 6000ms)!
      52 |     // debugging always takes longer than the test timeout.
      53 |     if (elapsedNS > timeoutNS && !IS_DEBUGGING) {
    > 54 |       throw new Error(
         |             ^
      55 |         `Test took too long (${elapsedNS / NS_PER_MS}ms > ${timeoutNS / NS_PER_MS}ms)!`,
      56 |       );
      57 |     }
      at Object.<anonymous> (spec/frontend/helpers/timeout.js:54:13)