tests: extend allow list in deletion test

[jcsp]

Problem

1ea5d8b tolerated this as an error message, but it can show up in logs as well.

Example failure: https://neon-github-public-dev.s3.amazonaws.com/reports/pr-8201/9780147712/index.html#testresult/263422f5f5f292ea/retries

Summary of changes

• Tolerate "failed to delete 1 objects" in pageserver logs, this occurs occasionally when injected failures exhaust deletion's retries.

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]

3006 tests run: 2891 passed, 0 failed, 115 skipped (full report)

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Code coverage* (full report)

• functions: 32.7% (6933 of 21219 functions)
• lines: 50.1% (54440 of 108708 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
eed4938 at 2024-07-04T15:53:10.342Z :recycle:}