[ET-VK] Only save_cache the first time

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This PR was created by the merge bot to help merge the original PR into the main branch. ghstack PR number: https://github.com/pytorch/executorch/pull/6966 ^ Please use this as the source of truth for the PR details, comments, and reviews ghstack PR base: https://github.com/pytorch/executorch/tree/gh/jorgep31415/125/base ghstack PR head: https://github.com/pytorch/executorch/tree/gh/jorgep31415/125/head Merge bot PR base: https://github.com/pytorch/executorch/tree/gh/jorgep31415/124/orig Merge bot PR head: https://github.com/pytorch/executorch/tree/gh/jorgep31415/125/orig @diff-train-skip-merge

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As of commit ee709a4499ce625d3171db49777bce264030dd2b with merge base 711f1c23d32acd798dabf0028b31e8fcb2c2487f (): :green_heart: Looks good so far! There are no failures yet. :green_heart:

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