Update G1MSM gas pricing

[MarekM25]

Changes

Applying the comment in the gas-repricing PR:
ethereum/EIPs#9116 (comment)

Types of changes

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• New feature (a non-breaking change that adds functionality)
• Breaking change (a change that causes existing functionality not to work as expected)
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Testing

Requires testing

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Notes on testing

Tested with Ethereum tests

Documentation

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