flaky unit/smoke tests

[noot]

I've noticed that some of the tests are flaky and sometimes fail and sometimes pass with no changes, locally and on CI.

ones I've encountered (will add if more are seen):

• tests::flashblocks::smoke_dynamic_base_flashblocks
• tests::flashblocks::smoke_dynamic_unichain_flashblocks
• tests::flashblocks::test_flashblock_min_filtering_flashblocks
• tests::flashblocks::unichain_dynamic_with_lag_flashblocks
• tests::flashtestations::test_flashtestations_block_proofs_flashblocks