Fix pipeline schedule resets to UTC on edit

Changelog: fixed

app/assets/javascripts/pages/projects/pipeline_schedules/shared/components/timezone_dropdown.js

 import initDeprecatedJQueryDropdown from '~/deprecated_jquery_dropdown';
 
-const defaultTimezone = { name: 'UTC', offset: 0 };
+const defaultTimezone = { identifier: 'Etc/UTC', name: 'UTC', offset: 0 };
 const defaults = {
   $inputEl: null,
   $dropdownEl: null,
@@ -70,7 +70,7 @@ export default class TimezoneDropdown {
 
   setDropdownValue(timezone) {
     this.$dropdownToggle.text(this.displayFormat(timezone));
-    this.$input.val(timezone.name);
+    this.$input.val(timezone.identifier);
   }
 
   handleDropdownChange({ selectedObj, e }) {

spec/frontend/pages/projects/pipeline_schedules/shared/components/timezone_dropdown_spec.js

@@ -38,14 +38,14 @@ describe('Timezone Dropdown', () => {
         const tzStr = '[UTC + 5.5] Sri Jayawardenepura';
         const tzValue = 'Asia/Colombo';
 
-        expect($inputEl.val()).toBe('UTC');
+        expect($inputEl.val()).toBe('Etc/UTC');
 
         $(`${tzListSel}:contains('${tzStr}')`, $wrapper).trigger('click');
 
         const val = $inputEl.val();
 
         expect(val).toBe(tzValue);
-        expect(val).not.toBe('UTC');
+        expect(val).not.toBe('Etc/UTC');
       });
 
       it('will format data array of timezones into a list of offsets', () => {
@@ -67,7 +67,7 @@ describe('Timezone Dropdown', () => {
         it('will default the timezone to UTC', () => {
           const tz = $inputEl.val();
 
-          expect(tz).toBe('UTC');
+          expect(tz).toBe('Etc/UTC');
         });
       });