kv/bulk: investigate failure on TestSSTBatcherPipelinedFlush with test tenants

`TestSSTBatcherPipelinedFlush` fails in external-process mode with some concerning logs:
```
W251027 23:06:02.607890 3535 kv/kvclient/kvtenant/connector.go:558 [T10,Vtest-tenant,range-lookup=/Meta2/Tenant/10/Table/104/1/0/0/NULL,nsql1,tenant-connector] 253 error issuing RangeLookup RPC: grpc: requested key /Meta2/Tenant/10/Table/104/1/0/0/NULL not fully contained in tenant keyspace /Tenant/1{0-1} [code 16/Unauthenticated]
W251027 23:06:02.608068 66 kv/bulk/sst_batcher.go:548 [-] 254 failed to lookup range cache entry for key /Tenant/10/Table/104/1/0/0: RangeIterator failed to seek to /Meta2/Tenant/10/Table/104/1/0/0/NULL: grpc: requested key /Meta2/Tenant/10/Table/104/1/0/0/NULL not fully contained in tenant keyspace /Tenant/1{0-1} [code 16/Unauthenticated]
```
We should investigate this.

I too have seen this test fail with shared-process mode, but only under stressrace:
```
sst_batcher_test.go:617:
Error Trace: pkg/kv/bulk/sst_batcher_test.go:617
Error: Condition never satisfied
Test: TestSSTBatcherPipelinedFlush
```

Jira issue: CRDB-55942

Epic CRDB-48568