fix flaky test

[trinity-1686a]

fix flakiness in test_garbage_collect_fails_to_run_delete_on_one_index introduced in #5380
the test depends of the order in which we iterate over the map. Fixed by finishing the iteration before aborting the gc run

[github-actions]

On SSD:

Average search latency is 1.0x that of the reference (lower is better).
Ref run id: 3278, ref commit: f49b253
Link

On GCS:

Average search latency is 0.972x that of the reference (lower is better).
Ref run id: 3280, ref commit: f49b253
Link