backupccl: `TestDataDriven_multiregion` stalls under `deadlock`

This test always seems to time out when run under `deadlock` (at least it does not complete within ~40 minutes). This is unusual for every other `TestDataDriven_` test -- they all comfortably meet the deadline. A deadlock does not seem to be actually occurring in this case, or at least one does not seem to be detected according to the logs. I am not sure if the test is simply slow. For now, I will skip this test under `deadlock` specifically.

[Example invocation on EngFlow](https://tanzanite.cluster.engflow.com/invocations/default/d935f665-b229-47e2-8bd4-3230b5624aca?testReportShard=33&testReportRun=1&testReportAttempt=0#targets-Ly9wa2cvY2NsL2JhY2t1cGNjbDpiYWNrdXBjY2xfdGVzdA==)

Jira issue: CRDB-35417