Fix flaky VSA feature test for predefined date range dropdown

What does this MR do and why?

Fixes flaky Value Stream Analytics feature test for predefined date range dropdown by setting time in spec to a specific date.

References

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• gitlab-org/quality/engineering-productivity/master-broken-incidents#10334 (closed)
• gitlab-org/quality/engineering-productivity/master-broken-incidents#10312 (closed)

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