…arian.yaml (#6015)

This PR re-applies the Go configuration restructuring from PR #5975,
nesting Go configuration under API entries. This PR will be merged right
before the companion configuration migration in google-cloud-go:
googleapis/google-cloud-go#14587 is merged.

<details>
<summary>This temporarily skips the integration test using
google-cloud-go.</summary>

Here is how GitHub Actions handles the subsequent
`create-issue-on-failure` job:

```yaml
  create-issue-on-failure:
    needs: [integration]
    if: ${{ always() && contains(needs.*.result, 'failure') && github.event_name == 'push' && github.ref == 'refs/heads/main' }}
```

1. **Dependency State**: Because `integration` has `if: false`, GitHub
Actions marks its final status as `skipped`.
2. **Evaluation**: By default, a job is skipped if its `needs`
dependency is skipped. However, because `create-issue-on-failure` uses
`always()`, GitHub evaluates its `if:` condition.
3. **Result**: The expression `needs.*.result` evaluates to
`['skipped']`. Since this array does not contain `'failure'`, the
`contains(...)` check evaluates to `false`.

As a result, the `create-issue-on-failure` job will be cleanly skipped
without creating any false alarm issues or causing workflow errors.
</details>

Fixes #5471