fix: use atomic.Int64 for shared counter

mentioned in merge request gitlab-org/duo-workflow/duo-workflow-executor!135 (merged)

mentioned in merge request gitlab-shell!1254 (merged)

mentioned in merge request gitlab-com/gl-infra/woodhouse!613

mentioned in merge request gitlab-com/gl-infra/platform/runway/example-service!262 (merged)

mentioned in merge request gitlab-org/cells/topology-service!180 (merged)

mentioned in merge request gitlab-elasticsearch-indexer!586 (merged)

mentioned in merge request release-tools!4002 (merged)

mentioned in merge request gitlab-com/gl-infra/cmbr!358 (merged)

mentioned in merge request gitlab-shell!1255 (closed)

mentioned in merge request gitlab-zoekt-indexer!400 (merged)

mentioned in merge request gitlab-pages!1130 (merged)

mentioned in merge request gitaly!7735 (merged)

mentioned in merge request container-registry!2186 (merged)