test: fix topology_custom dev regression failures

[darwin67]

Context

The dev-mode PR regression suite currently skips several inherited topology_custom tests in test/topology_custom/suite.yaml.

These were skipped while enabling full regression CI because they fail in the GitHub Actions dev build after the CI harness successfully starts and runs the suite.

Observed failure

Run: https://github.com/inngest/ssdb/actions/runs/26493036621/job/78015374770

Failing tests observed before the skip:

• topology_custom.test_different_group0_ids.1
• topology_custom.test_replace_with_same_ip_twice.1
• topology_custom.test_replace_with_encryption.1
• topology_custom.test_tablets.1

Representative symptoms:

• test_different_group0_ids raised HTTPError from decommission-node, but the assertion expected a message matching zero replica after the removal.
• test_tablets raised HTTPError, but the assertion expected a message matching Decommission failed.
• Replacement tests failed during topology replacement flows in dev CI.

Current workaround

test/topology_custom/suite.yaml has these tests under skip_in_dev so PR dev regression CI can continue running the rest of the topology-custom suite.

Done when

• Each skipped dev test is either fixed, moved to the intended mode, or documented as intentionally unsupported in dev mode.
• The skip_in_dev entries are removed or replaced with a documented permanent policy.
• PR regression CI remains green.