sql: sort rulesForRelease versions in descending order

Implementing fix from:
https://github.com/cockroachdb/cockroach/actions/runs/18817950946

Bug Summary
Location: `pkg/sql/schemachanger/scplan/plan.go:158-163`

Issue: The `rulesForReleases` array has incorrect ordering. Entries V25_2, V25_3, V25_4 are in ascending order, but the documented requirement (line 156-157) and the search logic in GetRulesRegistryForRelease() require descending order (newest first).

Current (incorrect):
```
{Latest},    // V26_1
{V25_2},     // ← wrong position
{V25_3},     // ← wrong position
{V25_4},     // ← wrong position
```

Should be (descending):
```
{Latest},    // V26_1
{V25_4},     // ← correct
{V25_3},     // ← correct
{V25_2},     // ← correct
```

Epic: None
Release note (bug fix): Fix rulesForReleases ordering.

Author: celiala