[TPU] update TPU benchmark threshold

[jcyang43]

Purpose

Update TPU benchmark expected threshold for stable version of torch_xla

Test Result

CI

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• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
• The test results, such as pasting the results comparison before and after, or e2e results
• (Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.
• (Optional) Release notes update. If your change is user facing, please update the release notes draft in the Google Doc.

[gemini-code-assist]

Code Review

This pull request updates the expected throughput threshold for a TPU benchmark. The change lowers the expected performance, which is a significant modification. My review focuses on improving the maintainability of this change by suggesting the addition of an inline comment to document the reason for this adjustment, preventing future confusion.

[gemini-code-assist]

This change lowers the expected throughput by over 10%, which is a significant performance regression. To ensure code maintainability and provide context for future developers, it's crucial to document the reason for this change directly in the configuration file. Adding a comment will clarify why the threshold was adjusted and prevent confusion or unnecessary investigations into this performance change in the future.

# Lowered from 10.0 to align with performance on the stable torch_xla version.
EXPECTED_THROUGHPUT=8.9

[yaochengji]

LGTM!