Update EIP-7667: Update eip-7667.md - add missing word

[NiloCK]

PR replaces A word of costs 512 gas with A word of calldata costs 512 gas.

[eth-bot]

File EIPS/eip-7667.md

Requires 1 more reviewers from @vbuterin

[github-actions[bot]]

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[github-actions[bot]]

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