test: disable large slru basebackup bench in ci

[VladLazar]

The test is flaky due to #7006.

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• If it is a core feature, I have added thorough tests.
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[github-actions]

2490 tests run: 2368 passed, 0 failed, 122 skipped (full report)

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Flaky tests (1)

Postgres 15

• test_timeline_size_quota_on_startup: release

Code coverage* (full report)

• functions: 28.8% (6982 of 24241 functions)
• lines: 47.4% (42872 of 90517 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
be5b9a1 at 2024-03-05T15:42:02.598Z :recycle:}