Enhance examples for @@SERVICENAME usage

[way0utwest]

Added examples for using @@SERVICENAME with default and named instances.

[prmerger-automator]

@way0utwest : Thanks for your contribution! The author(s) and reviewer(s) have been notified to review your proposed change.

[prmerger-automator]

@way0utwest : Thanks for your contribution! The author(s) and reviewer(s) have been notified to review your proposed change.

[learn-build-service-prod]

Learn Build status updates of commit 8a933c8:

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docs/t-sql/functions/servicename-transact-sql.md	✅Succeeded

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[v-dirichards]

@VanMSFT

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

[Copilot]

Pull request overview

This PR enhances the @@SERVICENAME documentation by expanding the Examples section to show expected output for both default and named SQL Server instances.

Changes:

• Refines the existing example description to explicitly target a default instance.
• Adds a second example demonstrating @@SERVICENAME behavior for a named instance (example output shows the instance name).

[rwestMSFT]

#reassign:rwestMSFT