fix: Update broken specs (#8651)

- Use fakeTimer for time.spec.js
- Use default sort as last_activity_at_desc
- Update specs for getAllConversations getter

app/javascript/dashboard/mixins/specs/time.spec.js

@@ -1,5 +1,4 @@
 import TimeMixin from '../time';
-import { format } from 'date-fns';
 
 describe('#messageStamp', () => {
   it('returns correct value', () => {
@@ -11,10 +10,20 @@ describe('#messageStamp', () => {
 });
 
 describe('#messageTimestamp', () => {
+  beforeEach(() => {
+    jest.useFakeTimers('modern');
+
+    const mockDate = new Date(2023, 4, 5);
+    jest.setSystemTime(mockDate);
+  });
+
+  afterEach(() => {
+    jest.useRealTimers();
+  });
+
   it('should return the message date in the specified format if the message was sent in the current year', () => {
-    const currentEpochTime = Math.floor(new Date().getTime() / 1000);
-    expect(TimeMixin.methods.messageTimestamp(currentEpochTime)).toEqual(
-      format(new Date(currentEpochTime * 1000), 'MMM d, yyyy')
+    expect(TimeMixin.methods.messageTimestamp(1680777464)).toEqual(
+      'Apr 6, 2023'
     );
   });
   it('should return the message date and time in a different format if the message was sent in a different year', () => {