tests: add a log allow list to stabilize benchmarks

[jcsp]

Problem

#7227 destabilized various tests in the performance suite, with log errors during shutdown. It's because we switched shutdown order to stop the storage controller before the pageservers.

Summary of changes

• Tolerate "connection failed" errors from pageservers trying to validation their deletion queue.

Checklist before requesting a review

• I have performed a self-review of my code.
• If it is a core feature, I have added thorough tests.
• Do we need to implement analytics? if so did you add the relevant metrics to the dashboard?
• If this PR requires public announcement, mark it with /release-notes label and add several sentences in this section.

Checklist before merging

• Do not forget to reformat commit message to not include the above checklist

[github-actions]

2798 tests run: 2648 passed, 0 failed, 150 skipped (full report)

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Code coverage* (full report)

• functions: 28.2% (6295 of 22343 functions)
• lines: 47.0% (44212 of 94145 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
154742f at 2024-03-26T16:43:21.887Z :recycle:}