Add info to event_time description

[rrg92]

Explicitly mention that event_time is in UTC

In most documents, I see that Microsoft mentions the timezone when a specific column is in UTC.

So, I added that to avoid any confusion.

[prmerger-automator]

@rrg92 : Thanks for your contribution! The author(s) have been notified to review your proposed change.

[learn-build-service-prod]

Learn Build status updates of commit f00514d:

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[ttorble]

@sravanisaluru

Can you review the proposed changes?

IMPORTANT: When the changes are ready for publication, adding a #sign-off comment is the best way to signal that the PR is ready for the review team to merge.

#label:"aq-pr-triaged"
@MicrosoftDocs/public-repo-pr-review-team

[learn-build-service-prod]

Learn Build status updates of commit c245cfe:

✅ Validation status: passed

File	Status	Preview URL	Details
docs/relational-databases/system-functions/sys-fn-get-audit-file-transact-sql.md	✅Succeeded

For more details, please refer to the build report.

For any questions, please:

• Try searching the learn.microsoft.com contributor guides
• Post your question in the Learn support channel