getFormFeedbacks test still flaky

[frankchn]

After #1620, there is still a chance that the getFormFeedbacks test is flaky if the creation time is exactly the same:

From https://github.com/opengovsg/FormSG/runs/2868044075?check_suite_focus=true

FAIL src/app/modules/feedback/__tests__/feedback.service.spec.ts
  ● feedback.service › getFormFeedbacks › should return correct feedback responses

    expect(received).toEqual(expected) // deep equality

    - Expected  - 4
    + Received  + 4

    @@ -9,22 +9,22 @@
            "index": 1,
            "rating": 5,
            "timestamp": 1624175860794,
          },
          Object {
    -       "comment": "cool form 1",
    +       "comment": "cool form 2",
            "date": "20 Jun 2021",
            "dateShort": "20 Jun",
            "index": 2,
    -       "rating": 4,
    +       "rating": 3,
            "timestamp": 1624175860794,
          },
          Object {
    -       "comment": "cool form 2",
    +       "comment": "cool form 1",
            "date": "20 Jun 2021",
            "dateShort": "20 Jun",
            "index": 3,
    -       "rating": 3,
    +       "rating": 4,
            "timestamp": 1624175860794,
          },
        ],
      }

      148 |       ).toFixed(2)
      149 |       expect(actualResult.isOk()).toEqual(true)
    > 150 |       expect(actualResult._unsafeUnwrap()).toEqual({
          |                                            ^
      151 |         average: expectedAverage,
      152 |         count: expectedCount,
      153 |         feedback: expectedFeedbackList,

      at src/app/modules/feedback/__tests__/feedback.service.spec.ts:150:44
      at fulfilled (src/app/modules/feedback/__tests__/feedback.service.spec.ts:24:58)
          at runMicrotasks (<anonymous>)