Ignore repair_run_by_cluster_v2 rows with no corresponding repair

[SesquipedalianDefenestrator]

When bad things (like Reaper filling the drive with logs) happen, it's possible to end up with repair_run_by_cluster_v2 rows with no corresponding repair row, which breaks Reaper. So, just skip them.

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[SesquipedalianDefenestrator]

I'm not actually sure if anything will clean up the repair_run_by_cluster_v2 rows, but I'm not sure it's a problem. The mismatch between repair_run and repair_run_by_cluster_v2 is frequent enough to be a pain (basically, a percentage of the time when anything goes wrong with the cluster and Reaper logs until the drive fills), but not often enough to generate measurable load.

[SesquipedalianDefenestrator]

Looks like there's an issue for this already as well: https://github.com/thelastpickle/cassandra-reaper/issues/1463

[Miles-Garnsey]

I'm looking at this, having some issues with my local setup as far as testing goes so bear with me while I try to work around them.