roachtest: fix configureGCPolicies to use system connection for zone config

[cockroach-teamcity]

The configureGCPolicies function in the mixed-version backup test
was using CommonTestUtils.Exec to run ALTER DATABASE bank CONFIGURE ZONE USING gc.ttlseconds = .... In shared-process deployment mode,
CommonTestUtils connects through the default service, which is the
virtual cluster (tenant). Since CONFIGURE ZONE is not supported
within virtual clusters, this caused the test to fail with:

pq: unimplemented: operation is unsupported within a virtual cluster

Fix this by using h.System.Exec() instead, which always connects
through the system tenant where zone configuration is allowed.

Resolves: #169309
Epic: none

Release note: None

Generated by Claude Code Auto-Solver
Co-Authored-By: Claude noreply@anthropic.com

---

 pkg/cmd/roachtest/tests/mixed_version_backup.go | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

This PR was auto-generated by issue-autosolve using Claude Code.
Please review carefully before approving.

[cockroach-teamcity]

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[dt]

I don't think this works: the the bank DB only exists in the tenant where we created / run it, so if the cluster does that in a main tenant instead of the system tenant, trying to configure a zone on bank in system tenant is just going to fail since there is no bank db there

[dt]

I don't think this works: the the bank DB only exists in the tenant where we created / run it, so if the cluster does that in a main tenant instead of the system tenant, trying to configure a zone on bank in system tenant is just going to fail since there is no bank db there

[dt]

maybe we should just only try to configure the zone on >24.1?

[github-actions]

[autosolve-response]

I've addressed the review comments and pushed updates.

Changes made:

## Summary

The reviewer (dt) correctly identified that `h.System.Exec()` would fail because the `bank` database only exists in the tenant, not in the system tenant.

**Fix:** Changed `configureGCPolicies` to use `h.Exec()` (which routes through the default/tenant service where `bank` exists) instead of `h.System.Exec()`. For older versions (pre-24.1) where zone config settings aren't enabled by default for virtual clusters, we first enable the necessary cluster settings (`sql.virtual_cluster.feature_access.zone_configs.enabled` and `sql.virtual_cluster.feature_access.zone_configs_unrestricted.enabled`) via `ALTER TENANT ... SET CLUSTER SETTING` on the system connection. This pattern matches the existing approach used in `mixed_version_change_replicas.go`.

CHANGES_RESULT - SUCCESS

Please review the updated code.

Workflow run

[dt]

how confident are we that this will make the line below work on old versions?

What about just skipping the zone config on older versions that don't support it?

[dt]

autosover: ping?