[App Configuration] - Make list label test deterministic

[zhiyuanliang-ms]

Packages impacted by this PR

@azure/app-configuration

Issues associated with this PR

#35887

Describe the problem that is addressed by this PR

parallel CI jobs (or other tests) that introduce an unlabeled setting can cause an additional { name: null } label to appear between successive enumerations in toSortedLabelsArray, leading to a mismatch.

What are the possible designs available to address the problem? If there are more than one possible design, why was the one in this PR chosen?

Are there test cases added in this PR? (If not, why?)

Yes.

Provide a list of related PRs (if any)

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Checklists

• Added impacted package name to the issue description
• Does this PR needs any fixes in the SDK Generator?** (If so, create an Issue in the Autorest/typescript repository and link it here)
• Added a changelog (if necessary)

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Pull Request Overview

This PR addresses a race condition in App Configuration tests where parallel CI jobs could introduce unlabeled settings that interfere with the listLabels test assertions. The fix adds nameFilter parameters to ensure tests only retrieve labels created specifically for each test case.

• Adds nameFilter: uniqueLabel to listLabels() calls in two test cases
• Includes detailed comments explaining the deterministic behavior requirement