changefeedccl: TestChangefeedNemeses and TestCatchupScanOrdering incorrectly skip using secondary tenants

**Describe the problem**

in `changefeedccl > nemeses_test.go`:

```go
// Tenant tests disabled because ALTER TABLE .. SPLIT is not
// supported with cluster virtualization:
//
// nemeses_test.go:39: pq: unimplemented: operation is unsupported inside virtual clusters
cdcTest(t, testFn, feedTestNoTenants)
```

Ditto in `validations_test.go`:

```go
// Tenant tests disabled because ALTER TABLE .. SPLIT is not
// supported with cluster virtualization:
//
// nemeses_test.go:39: pq: unimplemented: operation is unsupported inside virtual clusters
//
// TODO(knz): This seems incorrect, see issue #109417.
cdcTest(t, testFn, feedTestNoTenants)
```

**Expected behavior**

Since SPLIT AT can be used from secondary tenants (with suitable capability), this test should be made to work this way.

Epic: CRDB-26687

Jira issue: CRDB-30914