audit: gitlab prerelease check keep time/zone

[cho-m]

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes? Here's an example.
• Have you successfully run brew style with your changes locally?
• Have you successfully run brew typecheck with your changes locally?
• Have you successfully run brew tests with your changes locally?

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Not sure if this check does anything with change, or if it is a no-op.

The existing check has a problem where CI runner timezone can impact behavior of prerelease output. Date.parse will ignore the time/timezone and parse the date portion.

For example, Homebrew/homebrew-core#83805

[BrewTestBot]

Review period will end on 2021-08-26 at 03:13:25 UTC.

[BrewTestBot]

Review period ended.

[cho-m]

I think this should be ready to merge.

Not sure if possible to add test coverage. At least, the Ruby logic seems to work with arbitrary timestamps/timezones compared to original.

[MikeMcQuaid]

Thanks again @cho-m!