Geo: MetricsUpdateWorker encountering query conflicts when many checksums are nil

After resetting the checksums today on the secondary, we see a lot of these exceptions (Sentry: https://sentry.gitlap.com/gitlab/gitlabcom/issues/485519) in ProjectRegistryFinder#count_verified_wikis:

PG::TRSerializationFailure: ERROR:  canceling statement due to conflict with recovery
DETAIL:  User query might have needed to see row versions that must be removed.
CONTEXT:  Remote SQL command: SELECT project_id FROM public.project_features WHERE ((wiki_access_level = 0)) AND ((project_id = $1::integer))
: SELECT COUNT(*) FROM "project_registry" WHERE ("project_registry"."wiki_verification_checksum_sha" IS NOT NULL) AND (NOT (EXISTS (SELECT 1 FROM "gitlab_secondary"."project_features" WHERE "gitlab_secondary"."project_features"."wiki_access_level" = 0 AND "gitlab_secondary"."project_features"."project_id" = "project_registry"."project_id")))

This FDW query might be too much.