ci: relax ordering assertion in test_detached_drop_is_collected_on_next_attach

[davidhewitt]

Closes #6318

As per discussion in that thread, it's possible that better test isolation with cargo nextest is worth doing in CI. However, I think for now adding a retry loop is somewhat good enough to make the test suite run approximately correctly under cargo test.

[codspeed-hq]

Merging this PR will improve performance by 30.55%

⚠️ Unknown Walltime execution environment detected

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⚠️ Different runtime environments detected

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⚡ 5 improved benchmarks
✅ 142 untouched benchmarks

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	WallTime	nested_attach_scaling/empty_pool[1]	4 ns	3 ns	+33.33%
⚡	WallTime	nested_attach_scaling/empty_pool[2]	4 ns	3 ns	+33.33%
⚡	WallTime	nested_attach_scaling/sparse_pool[1]	4 ns	3 ns	+33.33%
⚡	WallTime	nested_attach_scaling/sparse_pool[2]	4 ns	3 ns	+33.33%
⚡	WallTime	nested_attach_scaling/empty_pool[4]	6 ns	5 ns	+20%

Tip

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_{Comparing davidhewitt:flaky-decref-next-attach (745a5a1) with main (dfdbc46)}