Add supressions to ARM StaticCacheModule

[GregoryComer]

Summary

Transformers 5.5 release changed one of the cache types to become a union. Not all union variants have .key and .value, so mypy complains. The code is sound, so just suppress the error since we know what the actual cache type is.

Test plan

Verified lint passes locally and in CI.

[pytorch-bot]

🔗 Helpful Links

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