Update cronstrue usage for internationalization

- use first entry of preferred locale to try to translate
  cronstrue output
- cronstrue defaults to en if language is not supported

ee/app/assets/javascripts/threat_monitoring/components/policy_editor/scan_execution_policy/lib/humanize.js

-import cronstrue from 'cronstrue';
+import cronstrue from 'cronstrue/i18n';
 import { convertToTitleCase, humanize } from '~/lib/utils/text_utility';
-import { sprintf, s__, n__ } from '~/locale';
+import { getPreferredLocales, sprintf, s__, n__ } from '~/locale';
 import { NO_RULE_MESSAGE } from './constants';
 
 const getActionText = (scanType) =>
@@ -34,7 +34,9 @@ const humanizeBranches = (originalBranches) => {
 };
 
 const humanizeCadence = (cadence) => {
-  return cronstrue.toString(cadence, { verbose: true }).toLowerCase();
+  return cronstrue
+    .toString(cadence, { locale: getPreferredLocales()[0], verbose: true })
+    .toLowerCase();
 };
 
 const humanizePipelineRule = (rule) => {

ee/spec/frontend/threat_monitoring/components/policy_editor/scan_execution_policy/lib/humanize_spec.js

@@ -34,6 +34,11 @@ describe('humanizeActions', () => {
 });
 
 describe('humanizeRules', () => {
+  beforeEach(() => {
+    // Need to spy on window.navigator.languages as it is read-only
+    jest.spyOn(window.navigator, 'languages', 'get').mockReturnValueOnce(['en']);
+  });
+
   it('returns the empty rules message in an Array if no rules are specified', () => {
     expect(humanizeRules([])).toStrictEqual([NO_RULE_MESSAGE]);
   });