Update Spanner Interval integration tests to call `UsingEmulator()`

The Spanner integrations tests have been written to expect particular behavior from the emulator, even it is an error, rather than just skipping the test altogether. See all the other UsingEmulator() calls in this file, for example. This allows us to learn when the emulator changes behavior and react accordingly, rather than just forgetting about the whole issue forever more.

[It also helped the emulator team, who (at least previously) ran our tests to check their implementation. Rather than just seeing successes no matter what they did, expecting the old (error) behavior allowed them to verify that things had indeed changed, and also to compare their new behavior to that of the service.]

Spanner Interval の統合テストファイルを見つけ、近くにある既存の UsingEmulator() 呼び出しを確認します。Interval の統合テストを同じパターンを使うように更新し、テストをスキップするのではなく、エミュレータのエラーに対する期待値を維持します。関連する Spanner 統合テストターゲットを実行し、エミュレータの動作が引き続き明示的にチェックされることを確認します。

索引モデルが issue の本文から書いたものです。