Make test_random_updates and test_read_at_max_lsn compatible with new compaction

[arpad-m]

Makes two of the tests work with the tiered compaction that I had to ignore in #7283.

The issue was that tiered compaction actually created image layers, but the keys didn't appear in them as collect_keyspace didn't include them. Not a compaction problem, but due to how the test is structured.

Fixes #7287

[github-actions]

2874 tests run: 2753 passed, 0 failed, 121 skipped (full report)

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Flaky tests (3)

Postgres 15

• test_gc_of_remote_layers: release
• test_vm_bit_clear_on_heap_lock: debug

Postgres 14

• test_create_churn_during_restart: release

Code coverage* (full report)

• functions: 28.2% (6580 of 23351 functions)
• lines: 46.9% (46744 of 99680 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
8df3169 at 2024-04-30T11:56:20.006Z :recycle:}

note a minor issue

[skyzh]

LGTM, but I feel a better fix is to temporary add this keyspace to collect_keyspace in testing mode, or have some tests with both random update + compaction in the future.

[arpad-m]

I feel a better fix is to temporary add this keyspace to collect_keyspace in testing mode, or have some tests with both random update + compaction in the future.

Yeah it's not perfect, but I'm sure there is other tests in the testsuite which do updates plus compaction. Note that the purpose of the tests is not to test compaction, otherwise probably greater care would have been taken to make the keys show up in collect_keyspace.

If you know of a good mechanism to make the keys be included in collect_keyspace, feel free to suggest it.