Skip race conditions tests

[rads-1996]

Description

Please add an informative description that covers that changes made by the pull request and link all relevant issues.

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• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
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[Copilot]

Pull request overview

This PR disables several filesystem-backed storage tests in azure-monitor-opentelemetry-exporter, and records the change in the package changelog.

Changes:

• Add @unittest.skip("transient storage") to three additional storage tests.
• Update CHANGELOG.md to note that transient storage tests are skipped.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 5 comments.

File	Description
sdk/monitor/azure-monitor-opentelemetry-exporter/tests/test_storage.py	Skips three additional tests related to LocalFileBlob/LocalFileStorage behaviors.
sdk/monitor/azure-monitor-opentelemetry-exporter/CHANGELOG.md	Notes the skipped transient storage tests in the Unreleased section.